[Openmcl-devel] slow read-char
erik at adaptations.com
Fri Jul 14 08:46:12 PDT 2006
Hi Takehiko -- you are not alone!
I recently experienced performance problems using READ (and probably
READ-BYTE) -- you can find the messages on the list from around June
21-25. My findings with Shark were similar to yours. When you look at
Shark's hierarchical view (don't remember what it is called) a lot of
the activity is underneath READ, where I saw the locking going on. In
my case it was some very high figure like 60% of activity associated
I figured it had something to do with making streams work with
multiple thread access, but didn't really pursue it further (rather
bookmarking it for future exploration, but I've got so much
bookmarked material that I'm really glad you encountered the same
issue and brought it up!)
My solution was to implement file caching in order to reduce the
amount of file reading that needs to happen during the live of the
application. This was in a web application which had run fine with a
lot of file reading on Allegro CL, but then slowed down a lot in
Openmcl. I went ahead and implemented file read and write caching and
performance immediately improved. In this case, these were changes
that I had planned on making one day if performance became in issue,
and work well in this context.
Of course, it would still be a treat to see READing be faster. The
proposed solution seems sensible -- streams could be marked for
operation in different contexts -- shared streams would need to be
controlled as currently, but private streams could only be accessed
by a single thread at a time, with the ability, of course, to control
which thread has access the the stream.
It is possible that I'll run up against this same issue with reading
and writing network connections -- I haven't Sharked this yet.
I suppose it is possible that there are some more hackish methods,
like building non-locking (and non-CL) read/write primitives that can
at least work with unix file descriptors and bytes (which is all I
BTW It may not be fair to compare Openmcl and Allegro CL in READ
performance, since Allegro is not native-threads on OS X.
On Jul 14, 2006, at 7:39 AM, Takehiko Abe wrote:
> Gary Byers wrote:
>> It's also worth checking to ensure that the locking is really
>> where the problem is. That seems likely, but it'd probably
>> be a good idea to run your test case through CHUD/Shark.
> I run the chud-metering.lisp for the first time. Still don't know
> how to read the result properly, but ccl::%unlock-recursive-lock
> (8.0%), SPmkunwind (7.4%) and ccl::%lock-recursive-lock (6.8%) are
> listed on the top.
>> The simplest way of avoiding it that comes to mind is to introduce
>> thread-private streams. I suspect (and this may vary a bit from
>> person to person) that most application-level streams are only
>> accessed from a single thread, and it might therefore be appropriate
>> to make "thread-private" streams be the default.
> I think the change would be nice -- I think it will be a boost
> for some applications... But, nobody has mentioned that read-char
> is slow before. So I'm not sure.
> On the other hand, I guess that if one wants to access a stream
> from multiple threads one has to lock it anyway regardless openmcl
> does its own locking or not.
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