Thought I'd pass this along, since the Linux vs FreeBSD performance
question comes up fairly regularly...

BTW, I've already asked about benchmarking with PostgreSQL, so please
don't go over there making trouble.

----- Forwarded message from Kris Kennaway <kris@obsecurity.org> -----

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Date: Sat, 24 Feb 2007 16:31:11 -0500
From: Kris Kennaway <kris@obsecurity.org>
To: current@FreeBSD.org, smp@FreeBSD.org, hackers@FreeBSD.org
User-Agent: Mutt/1.4.2.2i
Cc:
Subject: Progress on scaling of FreeBSD on 8 CPU systems
Precedence: list
Errors-To: owner-freebsd-current@freebsd.org

Now that the goals of the SMPng project are complete, for the past
year or more several of us have been working hard on profiling FreeBSD
in various multiprocessor workloads, and looking for performance
bottlenecks to be optimized.

We have recently made significant progress on optimizing for MySQL
running on an 8-core amd64 system. The graph of results may be found
here:

http://www.freebsd.org/~kris/scaling/scaling.png

This shows the graph of MySQL transactions/second performed by a
multi-threaded client workload against a local MySQL database with
varying numbers of client threads, with identically configured FreeBSD
and Linux systems on the same machine.

The test was run on FreeBSD 7.0, with the latest version of the ULE
2.0 scheduler, the libthr threading library, and an uncommitted patch
from Jeff Roberson [1] that addresses poor scalability of file
descriptor locking (using a new sleepable mutex primitive); this patch
is responsible for almost all of the performance and scaling
improvements measured. It also includes some other patches (collected
in my kris-contention p4 branch) that have been shown to help
contention in MySQL workloads in the past (including a UNIX domain
socket locking pushdown patch from Robert Watson), but these were
shown to only give small individual contributions, with a cumulative
effect on the order of 5-10%.

With this configuration we are able to achieve performance that is
consistent with Linux at peak (the graph shows Linux 2% faster, but
this is commensurate with the margin of error coming from variance
between runs, so more data is needed to distinguish them), with 8
client threads (=1 thread/CPU core), and significantly outperforms
Linux at higher than peak loads, when running on the same hardware.

Specifically, beyond 8 client threads FreeBSD has only minor
performance degradation (an 8% drop from peak throughput at 8 clients
to 20 clients), but Linux collapses immediately above 8 threads, and
above 14 threads asymptotes to essentially single-threaded levels. At
20 clients FreeBSD outperforms Linux by a factor of 4.

We see this result as part of the payoff we are seeing from the hard
work of many developers over the past 7 years. In particular it is a
significant validation of the SMP and locking strategies chosen for
the FreeBSD kernel in the post-FreeBSD 4.x world.

More configuration details and discussion about the benchmark may be
found here:

http://people.freebsd.org/~kris/scaling/mysql.html

Kris



----- End forwarded message -----

--
Jim C. Nasby, Database Architect decibel@decibel.org
Give your computer some brain candy! www.distributed.net Team #1828

Windows: "Where do you want to go today?"
Linux: "Where do you want to go tomorrow?"
FreeBSD: "Are you guys coming, or what?"

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> From: Kris Kennaway <kris@obsecurity.org>

> We have recently made significant progress on optimizing for MySQL
> running on an 8-core amd64 system. The graph of results may be found
> here:
>
> http://www.freebsd.org/~kris/scaling/scaling.png
>
> This shows the graph of MySQL transactions/second performed by a
> multi-threaded client workload against a local MySQL database with
> varying numbers of client threads, with identically configured FreeBSD
> and Linux systems on the same machine.

Interesting -- the MySQL/Linux graph is very similar to the graphs from
the .nl magazine posted last year. I think this suggests that the
"MySQL deficiency" was rather a performance bug in Linux, not in MySQL
itself ...

--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.

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Alvaro Herrera wrote:
> Interesting -- the MySQL/Linux graph is very similar to the graphs from
> the .nl magazine posted last year. I think this suggests that the
> "MySQL deficiency" was rather a performance bug in Linux, not in MySQL
> itself ...

The latest benchmark we did was both with Solaris and Linux on the same
box, both showed such a drop. So I doubt its "not in MySQL", although it
might be possible to fix the load MySQL's usage pattern poses on a
system, via the OS. And since MySQL 5.0.32 is less bad than 4.1.22 on
that system. We didn't have time to test 5.0.25 again, but .32 scaled
better, so at least some of the scaling issues where actually fixed in
MySQL itself.

Best regards,

Arjen

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On Fri, 2007-03-02 at 09:01, Alvaro Herrera wrote:
> > From: Kris Kennaway <kris@obsecurity.org>
>
> > We have recently made significant progress on optimizing for MySQL
> > running on an 8-core amd64 system. The graph of results may be found
> > here:
> >
> > http://www.freebsd.org/~kris/scaling/scaling.png
> >
> > This shows the graph of MySQL transactions/second performed by a
> > multi-threaded client workload against a local MySQL database with
> > varying numbers of client threads, with identically configured FreeBSD
> > and Linux systems on the same machine.
>
> Interesting -- the MySQL/Linux graph is very similar to the graphs from
> the .nl magazine posted last year. I think this suggests that the
> "MySQL deficiency" was rather a performance bug in Linux, not in MySQL
> itself ...

I rather think it's a combination of how MySQL does things and Linux not
being optimized to handle that situation.

It may well be that the fixes to BSD have simply moved the point at
which performance dives off quickly from 50 connections to 300 or
something.

I'd really like to see freebsd tested on the 32 thread Sun CPU that had
such horrible performance with linux, and with many more threads to see
if there's still a cliff there somewhere, and to see where postgresql's
cliff would be as well. After all, the most interesting part of
performance graphs are the ones you see when the system is heading into
overload.

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And here is that latest benchmark we did, using a 8 dual core opteron
Sun Fire x4600. Unfortunately PostgreSQL seems to have some difficulties
scaling over 8 cores, but not as bad as MySQL.

http://tweakers.net/reviews/674

Best regards,

Arjen

Arjen van der Meijden wrote:
> Alvaro Herrera wrote:
>> Interesting -- the MySQL/Linux graph is very similar to the graphs from
>> the .nl magazine posted last year. I think this suggests that the
>> "MySQL deficiency" was rather a performance bug in Linux, not in MySQL
>> itself ...
>
> The latest benchmark we did was both with Solaris and Linux on the same
> box, both showed such a drop. So I doubt its "not in MySQL", although it
> might be possible to fix the load MySQL's usage pattern poses on a
> system, via the OS. And since MySQL 5.0.32 is less bad than 4.1.22 on
> that system. We didn't have time to test 5.0.25 again, but .32 scaled
> better, so at least some of the scaling issues where actually fixed in
> MySQL itself.
>
> Best regards,
>
> Arjen
>
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>
> http://www.postgresql.org/about/donate
>

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Arjen van der Meijden wrote:
> And here is that latest benchmark we did, using a 8 dual core opteron
> Sun Fire x4600. Unfortunately PostgreSQL seems to have some difficulties
> scaling over 8 cores, but not as bad as MySQL.
>
> http://tweakers.net/reviews/674

ouch - do I read that right that even after tom's fixes for the
"regressions" in 8.2.0 we are still 30% slower then the -HEAD checkout
from the middle of the 8.2 development cycle ?


Stefan

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Stefan Kaltenbrunner wrote:
> ouch - do I read that right that even after tom's fixes for the
> "regressions" in 8.2.0 we are still 30% slower then the -HEAD checkout
> from the middle of the 8.2 development cycle ?

Yes, and although I tested about 17 different cvs-checkouts, Tom and I
weren't really able to figure out where "it" happened. So its a bit of a
mystery why the performance is so much worse.

Best regards,

Arjen

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Arjen van der Meijden wrote:
> And here is that latest benchmark we did, using a 8 dual core opteron
> Sun Fire x4600. Unfortunately PostgreSQL seems to have some difficulties
> scaling over 8 cores, but not as bad as MySQL.
>
> http://tweakers.net/reviews/674

Hmm - interesting reading as always Arjen.

Thanks for the notice on this.

--
Richard Huxton
Archonet Ltd

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Arjen van der Meijden wrote:
> Stefan Kaltenbrunner wrote:
>> ouch - do I read that right that even after tom's fixes for the
>> "regressions" in 8.2.0 we are still 30% slower then the -HEAD checkout
>> from the middle of the 8.2 development cycle ?
>
> Yes, and although I tested about 17 different cvs-checkouts, Tom and I
> weren't really able to figure out where "it" happened. So its a bit of a
> mystery why the performance is so much worse.

double ouch - losing that much in performance without an idea WHY it
happened is really unfortunate :-(


Stefan

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Stefan Kaltenbrunner <stefan@kaltenbrunner.cc> writes:
> Arjen van der Meijden wrote:
>> Stefan Kaltenbrunner wrote:
>>> ouch - do I read that right that even after tom's fixes for the
>>> "regressions" in 8.2.0 we are still 30% slower then the -HEAD checkout
>>> from the middle of the 8.2 development cycle ?
>>
>> Yes, and although I tested about 17 different cvs-checkouts, Tom and I
>> weren't really able to figure out where "it" happened. So its a bit of a
>> mystery why the performance is so much worse.

> double ouch - losing that much in performance without an idea WHY it
> happened is really unfortunate :-(

Keep in mind that Arjen's test exercises some rather narrow scenarios;
IIRC its performance is mostly determined by some complicated
bitmap-indexscan cases. So that "30% slower" bit certainly doesn't
represent an across-the-board figure. As best I can tell, the decisions
the planner happened to be making in late June were peculiarly nicely
suited to his test, but not so much for other cases.

regards, tom lane

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