Re: [HACKERS] kqueue

On Sat, Sep 29, 2018 at 7:51 PM Matteo Beccati <php(at)beccati(dot)com> wrote:
> On 28/09/2018 14:19, Thomas Munro wrote:
> > On Fri, Sep 28, 2018 at 11:09 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
> >> On 2018-09-28 10:55:13 +1200, Thomas Munro wrote:
> >>> Matteo Beccati reported a 5-10% performance drop on a
> >>> low-end Celeron NetBSD box which we have no explanation for, and we
> >>> have no reports from server-class machines on that OS -- so perhaps we
> >>> (or the NetBSD port?) should consider building with WAIT_USE_POLL on
> >>> NetBSD until someone can figure out what needs to be fixed there
> >>> (possibly on the NetBSD side)?
> >>
> >> Yea, I'm not too worried about that. It'd be great to test that, but
> >> otherwise I'm also ok to just plonk that into the template.
> >
> > Thanks for the review! Ok, if we don't get a better idea I'll put
> > this in src/template/netbsd:
> >
> > CPPFLAGS="$CPPFLAGS -DWAIT_USE_POLL"
>
> A quick test on a 8 vCPU / 4GB RAM virtual machine running a fresh
> install of NetBSD 8.0 again shows that kqueue is consistently slower
> running pgbench vs unpatched master on tcp-b like pgbench workloads:
>
> ~1200tps vs ~1400tps w/ 96 clients and threads, scale factor 10
>
> while on select only benchmarks the difference is below the noise floor,
> with both doing roughly the same ~30k tps.
>
> Out of curiosity, I've installed FreBSD on an identically specced VM,
> and the select benchmark was ~75k tps for kqueue vs ~90k tps on
> unpatched master, so maybe there's something wrong I'm doing when
> benchmarking. Could you please provide proper instructions?

Ouch. What kind of virtualisation is this? Which version of FreeBSD?
Not sure if it's relevant, but do you happen to see gettimeofday()
showing up as a syscall, if you truss a backend running pgbench?

--
Thomas Munro
http://www.enterprisedb.com