Hi,
In my code, I need to concat two buffer into one. I take following
steps:
1 malloc a new space
2 copy two buffers over,
3. and then free the originial two buffers.
I put timer on each step. And I found that under some stress
condition(cpu intensive, lots of memory used), the last step took a
lot more time than step 1 and 2. Did anyone know what could be the
reason?
18  1444 
Lianjun Jiang <li******@gmail.comwrites:
In my code, I need to concat two buffer into one. I take following
steps:
1 malloc a new space
2 copy two buffers over,
3. and then free the originial two buffers.
I put timer on each step. And I found that under some stress
condition(cpu intensive, lots of memory used), the last step took a
lot more time than step 1 and 2. Did anyone know what could be the
reason?
It's extremely system-specific.
The C standard says absolutely nothing about the performance of malloc
and free (or of anything else, for that matter).
malloc and free have to manipulate whatever internal data structures
the implementation uses for memory allocation. It's possible that
malloc() merely has to find the first available free chunk of at least
the requested size, but free() has to do considerable work to
rearrange things (merging adjacent free chunks, updating statistics,
whatever) for future allocations. But that's pure speculation on my
part.
--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
On 28 Jun, 00:03, Lianjun Jiang <lianj...@gmail.comwrote:
Hi,
In my code, I need to concat two buffer into one. I take following
steps:
1 malloc a new space
2 copy two buffers over,
3. and then free the originial two buffers.
I put timer on each step. And I found that under some stress
condition(cpu intensive, lots of memory used), the last step took a
lot more time than step 1 and 2. Did anyone know what could be the
reason?
I have no idea why free takes a long time but one suggestion
is that you use realloc to make the first buffer large
enough to also fit the second buffer , then add the
second buffer to the end of the first and free the second.
Perhaps this will run faster.
Are you sure that the timer you're using is reliable ?
On Jun 27, 4:58 pm, Spiros Bousbouras <spi...@gmail.comwrote:
On 28 Jun, 00:03, Lianjun Jiang <lianj...@gmail.comwrote:
Hi,
In my code, I need to concat two buffer into one. I take following
steps:
1 malloc a new space
2 copy two buffers over,
3. and then free the originial two buffers.
I put timer on each step. And I found that under some stress
condition(cpu intensive, lots of memory used), the last step took a
lot more time than step 1 and 2. Did anyone know what could be the
reason?
I have no idea why free takes a long time but one suggestion
is that you use realloc to make the first buffer large
enough to also fit the second buffer , then add the
second buffer to the end of the first and free the second.
Perhaps this will run faster.
Are you sure that the timer you're using is reliable ?
At first, my implementation is using realloc, and then realloc takes
similar time as free. I think that is because realloc need one free
call, too. So I used current approach, and kind of verify it is the
free that slow down realloc.
For the timers, it at least provides very consistent result.
On Jun 27, 4:03 pm, Lianjun Jiang <lianj...@gmail.comwrote:
In my code, I need to concat two buffer into one. I take following
steps:
1 malloc a new space
2 copy two buffers over,
3. and then free the originial two buffers.
I put timer on each step. And I found that under some stress
condition(cpu intensive, lots of memory used), the last step took a
lot more time than step 1 and 2. Did anyone know what could be the
reason?
In balanced heap implementations, the cost of free() and malloc()
should be *roughly* the same. free() needs to merge the memory with
adjacent free buffers if possible, and then update the new free
buffers relative to whatever structures they exist in to assist the
malloc() function to find them quickly.
--
Paul Hsieh http://www.pobox.com/~qed/ http://bstring.sf.net/
Lianjun Jiang wrote:
>
In my code, I need to concat two buffer into one. I take following
steps:
1 malloc a new space
2 copy two buffers over,
3. and then free the originial two buffers.
I put timer on each step. And I found that under some stress
condition(cpu intensive, lots of memory used), the last step took
a lot more time than step 1 and 2. Did anyone know what could be
the reason?
Yes. It usually depends on the number of malloced pieces in effect
at the time and the effort required to detect and join them. I
wrote nmalloc to avoid it (and a few other problems). See:
<http://cbfalconer.home.att.net/download/>
for an (almost) standard C implementation for DJGPP and others.
--
<http://www.cs.auckland.ac.nz/~pgut001/pubs/vista_cost.txt>
<http://www.securityfocus.com/columnists/423>
<http://www.aaxnet.com/editor/edit043.html>
cbfalconer at maineline dot net
--
Posted via a free Usenet account from http://www.teranews.com we******@gmail.com wrote:
Lianjun Jiang <lianj...@gmail.comwrote:
>In my code, I need to concat two buffer into one. I take following
steps:
1 malloc a new space
2 copy two buffers over,
3. and then free the originial two buffers.
I put timer on each step. And I found that under some stress
condition(cpu intensive, lots of memory used), the last step took a
lot more time than step 1 and 2. Did anyone know what could be the
reason?
In balanced heap implementations, the cost of free() and malloc()
should be *roughly* the same. free() needs to merge the memory with
adjacent free buffers if possible, and then update the new free
buffers relative to whatever structures they exist in to assist the
malloc() function to find them quickly.
I don't know what you mean by 'balanced heap', but in general the
cause is the excessive searching for adjacent blocks to merge
during the free operation. This is often an O(n) operation. In
nmalloc, it is cut to O(1).
--
<http://www.cs.auckland.ac.nz/~pgut001/pubs/vista_cost.txt>
<http://www.securityfocus.com/columnists/423>
<http://www.aaxnet.com/editor/edit043.html>
cbfalconer at maineline dot net
--
Posted via a free Usenet account from http://www.teranews.com
"CBFalconer" <cb********@yahoo.comwrote in message
news:46***************@yahoo.com...
Lianjun Jiang wrote:
>>
In my code, I need to concat two buffer into one. I take following
steps:
1 malloc a new space
2 copy two buffers over,
3. and then free the originial two buffers.
I put timer on each step. And I found that under some stress
condition(cpu intensive, lots of memory used), the last step took
a lot more time than step 1 and 2. Did anyone know what could be
the reason?
Yes. It usually depends on the number of malloced pieces in effect
at the time and the effort required to detect and join them. I
wrote nmalloc to avoid it (and a few other problems). See:
<http://cbfalconer.home.att.net/download/>
for an (almost) standard C implementation for DJGPP and others.
Although in most cases I agree with you, how do you find an
almost because I wrote it, appropriate for clc?
Barry wrote:
"CBFalconer" <cb********@yahoo.comwrote in message
news:46***************@yahoo.com...
>Lianjun Jiang wrote:
>>In my code, I need to concat two buffer into one. I take following
steps:
1 malloc a new space
2 copy two buffers over,
3. and then free the originial two buffers.
I put timer on each step. And I found that under some stress
condition(cpu intensive, lots of memory used), the last step took
a lot more time than step 1 and 2. Did anyone know what could be
the reason?
Yes. It usually depends on the number of malloced pieces in effect
at the time and the effort required to detect and join them. I
wrote nmalloc to avoid it (and a few other problems). See:
<http://cbfalconer.home.att.net/download/>
for an (almost) standard C implementation for DJGPP and others.
Although in most cases I agree with you, how do you find an
almost because I wrote it, appropriate for clc?
Can you explain what's wrong with the message?
Or you think it is forbidden to speak about what one's writes
in this newsgroup?
jacob
"jacob navia" <ja***@jacob.remcomp.frwrote in message
news:46**********************@news.orange.fr...
Barry wrote:
>"CBFalconer" <cb********@yahoo.comwrote in message
news:46***************@yahoo.com...
>>Lianjun Jiang wrote:
In my code, I need to concat two buffer into one. I take following
steps:
1 malloc a new space
2 copy two buffers over,
3. and then free the originial two buffers.
I put timer on each step. And I found that under some stress
condition(cpu intensive, lots of memory used), the last step took
a lot more time than step 1 and 2. Did anyone know what could be
the reason?
Yes. It usually depends on the number of malloced pieces in effect
at the time and the effort required to detect and join them. I
wrote nmalloc to avoid it (and a few other problems). See:
<http://cbfalconer.home.att.net/download/>
for an (almost) standard C implementation for DJGPP and others.
Although in most cases I agree with you, how do you find an
almost because I wrote it, appropriate for clc?
Can you explain what's wrong with the message?
Or you think it is forbidden to speak about what one's writes
in this newsgroup?
jacob
I wrote my response in simple English. What part confuses you?
Barry wrote:
"jacob navia" <ja***@jacob.remcomp.frwrote in message
news:46**********************@news.orange.fr...
>Barry wrote:
>>"CBFalconer" <cb********@yahoo.comwrote in message
news:46***************@yahoo.com...
Lianjun Jiang wrote:
In my code, I need to concat two buffer into one. I take following
steps:
1 malloc a new space
2 copy two buffers over,
3. and then free the originial two buffers.
I put timer on each step. And I found that under some stress
condition(cpu intensive, lots of memory used), the last step took
a lot more time than step 1 and 2. Did anyone know what could be
the reason?
Yes. It usually depends on the number of malloced pieces in effect
at the time and the effort required to detect and join them. I
wrote nmalloc to avoid it (and a few other problems). See:
<http://cbfalconer.home.att.net/download/>
for an (almost) standard C implementation for DJGPP and others.
Although in most cases I agree with you, how do you find an
almost because I wrote it, appropriate for clc?
Can you explain what's wrong with the message?
Or you think it is forbidden to speak about what one's writes
in this newsgroup?
jacob
I wrote my response in simple English. What part confuses you?
You wrote:
"Although in most cases I agree with you, how do you find an
almost because I wrote it, appropriate for clc?"
Parse error. "How do you find an almost" ???
Something is missing I would say.
"jacob navia" <ja***@jacob.remcomp.frwrote in message
news:46***********************@news.orange.fr...
Barry wrote:
>"jacob navia" <ja***@jacob.remcomp.frwrote in message
news:46**********************@news.orange.fr...
>>Barry wrote:
"CBFalconer" <cb********@yahoo.comwrote in message
news:46***************@yahoo.com...
Lianjun Jiang wrote:
>In my code, I need to concat two buffer into one. I take following
>steps:
>1 malloc a new space
>2 copy two buffers over,
>3. and then free the originial two buffers.
>I put timer on each step. And I found that under some stress
>condition(cpu intensive, lots of memory used), the last step took
>a lot more time than step 1 and 2. Did anyone know what could be
>the reason?
Yes. It usually depends on the number of malloced pieces in effect
at the time and the effort required to detect and join them. I
wrote nmalloc to avoid it (and a few other problems). See:
>
<http://cbfalconer.home.att.net/download/>
>
for an (almost) standard C implementation for DJGPP and others.
>
Although in most cases I agree with you, how do you find an
almost because I wrote it, appropriate for clc?
Can you explain what's wrong with the message?
Or you think it is forbidden to speak about what one's writes
in this newsgroup?
jacob
I wrote my response in simple English. What part confuses you?
You wrote:
"Although in most cases I agree with you, how do you find an
almost because I wrote it, appropriate for clc?"
Parse error. "How do you find an almost" ???
Something is missing I would say.
"How do you find an almost," is not what it says. Had I written:
How do you find a purple polka dot elephant in a bowl of cherries?
Would you ask how do you find a purple?
In article <13*************@corp.supernews.com>,
Barry <ba****@nullhighstream.netwrote:
>>I wrote my response in simple English. What part confuses you?
>You wrote:
"Although in most cases I agree with you, how do you find an
almost because I wrote it, appropriate for clc?"
Parse error. "How do you find an almost" ???
Something is missing I would say.
>"How do you find an almost," is not what it says. Had I written:
How do you find a purple polka dot elephant in a bowl of cherries?
Would you ask how do you find a purple?
I'm a native speaker of English, and I can't make any sense of your
sentence.
-- Richard
--
"Consideration shall be given to the need for as many as 32 characters
in some alphabets" - X3.4, 1963. ri*****@cogsci.ed.ac.uk (Richard Tobin) wrote:
In article <13*************@corp.supernews.com>,
Barry <ba****@nullhighstream.netwrote:
>I wrote my response in simple English. What part confuses you?
You wrote:
"Although in most cases I agree with you, how do you find an
almost because I wrote it, appropriate for clc?"
Parse error. "How do you find an almost" ???
Something is missing I would say.
"How do you find an almost," is not what it says. Had I written:
How do you find a purple polka dot elephant in a bowl of cherries?
Would you ask how do you find a purple?
I'm a native speaker of English, and I can't make any sense of your
sentence.
I'm not a native speaker of English, and I find that sentence completely
understandable provided it is not ripped cruelly out of context.
Richard
Barry wrote:
"CBFalconer" <cb********@yahoo.comwrote in message
.... snip ...
>>
Yes. It usually depends on the number of malloced pieces in effect
at the time and the effort required to detect and join them. I
wrote nmalloc to avoid it (and a few other problems). See:
<http://cbfalconer.home.att.net/download/>
for an (almost) standard C implementation for DJGPP and others.
Although in most cases I agree with you, how do you find an
almost because I wrote it, appropriate for clc?
Please attempt to write a fully standard general malloc package.
Can't be done. That is one reason it is part of the
implementation.
--
<http://www.cs.auckland.ac.nz/~pgut001/pubs/vista_cost.txt>
<http://www.securityfocus.com/columnists/423>
<http://www.aaxnet.com/editor/edit043.html>
cbfalconer at maineline dot net
--
Posted via a free Usenet account from http://www.teranews.com
Richard Tobin wrote:
Barry <ba****@nullhighstream.netwrote:
>>>I wrote my response in simple English. What part confuses you?
>>You wrote:
"Although in most cases I agree with you, how do you find an
almost because I wrote it, appropriate for clc?"
Parse error. "How do you find an almost" ???
Something is missing I would say.
>"How do you find an almost," is not what it says. Had I written:
How do you find a purple polka dot elephant in a bowl of cherries?
Would you ask how do you find a purple?
I'm a native speaker of English, and I can't make any sense of your
sentence.
I am also (a native speaker), yet I can make sense out of it. It
is an effort, but possible.
BTW someone has been grossly careless in snipping attributions for
quoted material.
--
<http://www.cs.auckland.ac.nz/~pgut001/pubs/vista_cost.txt>
<http://www.securityfocus.com/columnists/423>
<http://www.aaxnet.com/editor/edit043.html>
cbfalconer at maineline dot net
--
Posted via a free Usenet account from http://www.teranews.com
"CBFalconer" <cb********@yahoo.comwrote in message
news:46***************@yahoo.com...
Barry wrote:
>"CBFalconer" <cb********@yahoo.comwrote in message
... snip ...
>>>
Yes. It usually depends on the number of malloced pieces in effect
at the time and the effort required to detect and join them. I
wrote nmalloc to avoid it (and a few other problems). See:
<http://cbfalconer.home.att.net/download/>
for an (almost) standard C implementation for DJGPP and others.
Although in most cases I agree with you, how do you find an
almost because I wrote it, appropriate for clc?
Please attempt to write a fully standard general malloc package.
Can't be done. That is one reason it is part of the
implementation.
Chuck, the post was partially in gest because you are typically the
first person to point out off topic posts. I didn't expect it to be a big
deal :-).
Barry wrote:
"CBFalconer" <cb********@yahoo.comwrote in message
>Barry wrote:
>>"CBFalconer" <cb********@yahoo.comwrote in message
... snip ...
>>>>
Yes. It usually depends on the number of malloced pieces in
effect at the time and the effort required to detect and join
them. I wrote nmalloc to avoid it (and a few other problems).
See:
<http://cbfalconer.home.att.net/download/>
for an (almost) standard C implementation for DJGPP and others.
Although in most cases I agree with you, how do you find an
almost because I wrote it, appropriate for clc?
Please attempt to write a fully standard general malloc package.
Can't be done. That is one reason it is part of the
implementation.
Chuck, the post was partially in gest because you are typically the
first person to point out off topic posts. I didn't expect it to be
a big deal :-).
OK. However, I did refrain from posting the code here. :-)
--
<http://www.cs.auckland.ac.nz/~pgut001/pubs/vista_cost.txt>
<http://www.securityfocus.com/columnists/423>
<http://www.aaxnet.com/editor/edit043.html>
cbfalconer at maineline dot net
--
Posted via a free Usenet account from http://www.teranews.com
On Jun 27, 7:40 pm, CBFalconer <cbfalco...@yahoo.comwrote:
websn...@gmail.com wrote:
Lianjun Jiang <lianj...@gmail.comwrote:
In my code, I need to concat two buffer into one. I take following
steps:
1 malloc a new space
2 copy two buffers over,
3. and then free the originial two buffers.
I put timer on each step. And I found that under some stress
condition(cpu intensive, lots of memory used), the last step took a
lot more time than step 1 and 2. Did anyone know what could be the
reason?
In balanced heap implementations, the cost of free() and malloc()
should be *roughly* the same. free() needs to merge the memory with
adjacent free buffers if possible, and then update the new free
buffers relative to whatever structures they exist in to assist the
malloc() function to find them quickly.
I don't know what you mean by 'balanced heap',
I mean 'balanced (heap) *implementation*'. Balanced, as in, one
operation is not penalized for the performance of another. For
example, its easy to make a super-fast malloc with a correspondingly
super-slow free and vice-versa. You can argue that the System V
implementation, for example, does favor malloc over free.
[...] but in general the
cause is the excessive searching for adjacent blocks to merge
during the free operation. This is often an O(n) operation. In
nmalloc, it is cut to O(1).
Right, but even being O(1), its not necessarily that fast. The OP is
talking real numbers, not just the theoretical stuff. Personally,
I've measured various implementations of malloc and free to be in the
100 clocks (on an Athlon CPU) kind of range (my recollection from
looking through your sources, is that you should have similar
performance), indicating that heap operations are worth minimizing.
But even in fair implementations you can see how mallocs from a fresh
heap might be fast-pathed and may be very fast when you measure it
directly under a simplistic test scenario. But the compiler developer
may have been lazy or it just might be difficult to implement a
corresponding fast-path for free (or perhaps its only fast-path if you
treat the heap like a stack, which you are unlikely to do, for
example, if you are allocating and deallocating an array of elements.)
--
Paul Hsieh http://www.pobox.com/~qed/ http://bstring.sf.net/ This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
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