| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Matteo Beccati <php(at)beccati(dot)com> |
| Cc: | Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Mateusz Guzik <mjguzik(at)gmail(dot)com>, Keith Fiske <keith(at)omniti(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Marko Tiikkaja <marko(at)joh(dot)to>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Noah Misch <noah(at)leadboat(dot)com> |
| Subject: | Re: [HACKERS] kqueue |
| Date: | 2018-10-01 17:28:03 |
| Message-ID: | 20181001172803.6r4nqkuzbop4tnrh@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
On 2018-10-01 19:25:45 +0200, Matteo Beccati wrote:
> On 01/10/2018 01:09, Thomas Munro wrote:
> > I don't know why the existence of the kqueue should make recvfrom()
> > slower on the pgbench side. That's probably something to look into
> > off-line with some FreeBSD guru help. Degraded performance for
> > clients on the same machine does seem to be a show stopper for this
> > patch for now. Thanks for testing!
>
> Glad to be helpful!
>
> I've tried running pgbench from a separate VM and in fact kqueue
> consistently takes the lead with 5-10% more tps on select/prepared pgbench
> on NetBSD too.
>
> What I have observed is that sys cpu usage is ~65% (35% idle) with kqueue,
> while unpatched master averages at 55% (45% idle): relatively speaking
> that's almost 25% less idle cpu available for a local pgbench to do its own
> stuff.
This suggest that either the the wakeup logic between kqueue and poll,
or the internal locking could be at issue. Is it possible that poll
triggers a directed wakeup path, but kqueue doesn't?
Greetings,
Andres Freund
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