Horton

Re: gettimeofday is at the end of its usefulness?

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Greg Stark <stark@mit.edu>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2014-05-14T11:41:26Z
Lists: pgsql-hackers 
On Tue, May 13, 2014 at 11:34 PM, Greg Stark <stark@mit.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

Commits

  1. Use clock_gettime(), if available, in instr_time measurements.