From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Greg Stark <stark(at)mit(dot)edu> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: gettimeofday is at the end of its usefulness? |
Date: | 2014-05-14 11:41:26 |
Message-ID: | CA+TgmoZyAACNS2SD48804BQeTz5DaS2WNLZx-rmFXCLYBJm=Fw@mail.gmail.com |
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Lists: | pgsql-hackers |
On Tue, May 13, 2014 at 11:34 PM, Greg Stark <stark(at)mit(dot)edu> wrote:
> I always assumed the kernel used rdtsc to implement some of the high
> performance timers. It can save the current time in a mapped page when
> it schedules a process and then in the vdso syscall (ie in user-space)
> it can use rdtsc to calculate the offset needed to adjust that
> timestamp to the current time. This seems consistent with your
> calculations that showed the 40ns overhead with +/- 10ns precision.
Crazy idea: Instead of trying to time precisely the amount of time we
spend in each node, configure a very-high frequency timer interrupt
(or background thread?) that does:
SomeGlobalVariablePointingToTheCurrentNode->profiling_counter++;
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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