From: Florian Weimer <fw@deneb.enyo.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Haribabu Kommi <kommi.haribabu@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: gettimeofday is at the end of its usefulness?
Date: Fri, 13 Jan 2017 21:48:51 +0100
Message-ID: <87wpdy1ya4.fsf@mid.deneb.enyo.de> (raw)
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* Tom Lane:
> Florian Weimer <fw@deneb.enyo.de> writes:
>> * Tom Lane:
>>> On Linux (RHEL6, 2.4GHz x86_64), I find that gettimeofday(),
>>> clock_gettime(CLOCK_MONOTONIC), and clock_gettime(CLOCK_REALTIME)
>>> all take about 40ns. Of course gettimeofday() only has 1us resolution,
>>> but the other two have perhaps 10ns resolution (I get no duplicate
>>> readings in a tight loop).
>
>> Isn't this very specific to kernel and glibc versions, depending on
>> things like CONFIG_HZ settings and what level of vDSO support has been
>> backported?
>
> No doubt, but I have yet to find a platform where clock_gettime() exists
> but performs worse than gettimeofday(). Do you know of one?
ppc64le with all the vDSO fixes for clock_gettime?
glibc has some test cases which fail because clock_gettime gives
inconsistent results. This has been fixed in current kernels, but I
don't know if everyone uses them.
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To: pgsql-hackers@postgresql.org
Cc: fw@deneb.enyo.de, tgl@sss.pgh.pa.us, kommi.haribabu@gmail.com
Subject: Re: gettimeofday is at the end of its usefulness?
In-Reply-To: <87wpdy1ya4.fsf@mid.deneb.enyo.de>
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