Re: Spin Lock sleep resolution

On 18.06.2013 10:52, David Gould wrote:
> On Tue, 18 Jun 2013 10:09:55 +0300
> Heikki Linnakangas<hlinnakangas(at)vmware(dot)com> wrote:
>
>> I repeated these pgbench tests I did earlier:
>>
>> http://www.postgresql.org/message-id/5190E17B.9060804@vmware.com
>>
>> I concluded in that thread that on this platform, the TAS_SPIN macro
>> really needs a non-locked test before the locked one. That fixes the big
>> fall in performance with more than 28 clients.
> ...
>> I wasn't expecting much of a gain from this, just wanted to verify that
>> it's not making things worse. So looks good to me.
>
> Thanks for the followup, and I really like your graph, it looks exactly
> like what we were hitting. My client ended up configuring around it
> and adding more hosts so the urgency to run more tests sort of declined,
> although I think we still hit it from time to time.

Oh, interesting. What kind of hardware are you running on? To be honest,
I'm not sure what my test hardware is, it's managed by another team
across the world, but /proc/cpuinfo says:

model name : Intel(R) Xeon(R) CPU E5-4640 0 @ 2.40GHz

And it's running in a virtual machine on VMware; that might also be a
factor.

It would be good to test the TAS_SPIN nonlocked patch on a variety of
systems. The comments in s_lock.h say that on Opteron, the non-locked
test is a huge loss. In particular, would be good to re-test that on a
modern AMD system.

> If you would like to point me at or send me the latest flavor of the patch
> it may be timely for me to test again. Especially if this is a more or less
> finished version, we are about to roll out a new build to all these hosts
> and I'd be happy to try to incorporate this patch and get some production
> experience with it on 80 core hosts.

Jeff's patch is here:
http://www.postgresql.org/message-id/CAMkU=1xtP+3UWL6dg10rDRtMA28zy-9ujrOxNuST_r3zOdpNxg@mail.gmail.com.
My non-locked TAS_SPIN patch is the one-liner here:
http://www.postgresql.org/message-id/519A938A.1070903@vmware.com

Thanks!

- Heikki