From: Richard Cochran <richardcochran@gmail.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: linux-kernel@vger.kernel.org, Kumar Sundararajan <kumar@fb.com>,
john stultz <johnstul@us.ibm.com>, Arun Sharma <asharma@fb.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 1/4] Add clock_gettime_ns syscall
Date: Tue, 27 Dec 2011 08:25:11 +0100 [thread overview]
Message-ID: <20111227072511.GA2250@netboy.at.omicron.at> (raw)
In-Reply-To: <16ecaa6abb8b7a25ef31970f71a42c7e2ba5416c.1324831829.git.luto@amacapital.net>
On Sun, Dec 25, 2011 at 08:51:00AM -0800, Andy Lutomirski wrote:
>
> This interface intentionally does not support sub-nanosecond
> precision. For one thing, light only travels about a foot per
> nanosecond, so nanoseconds are really pretty good for networking
> purposes. For another, 2^64 picoseconds (say) is a short enough
> interval to be inconvenient. If anyone needs sub-nanosecond
> precision for anything other than profiling, they're welcome to
> figure out an appropriate interface. For very precise profiling,
> "what time is it" is the wrong question, anyway -- modern CPUs can
> reorder things across time scales much longer than a nanosecond.
This paragraph probably should be updated, since you did add a padding
field for future sub-nanosecond reporting.
Also, on re-reading this, it seems silly to be to introduce a function
called "clock_gettime_ns" and then to say that this function cannot
answer the question, what time is it?
If the interface is a profiling only interface, then the name should
reflect this fact.
Thanks,
Richard
next prev parent reply other threads:[~2011-12-27 7:25 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-25 16:50 [PATCH 0/4] clock_gettime_ns and x86-64 optimizations Andy Lutomirski
2011-12-25 16:51 ` [PATCH 1/4] Add clock_gettime_ns syscall Andy Lutomirski
2011-12-27 7:25 ` Richard Cochran [this message]
2011-12-28 19:02 ` Arun Sharma
[not found] ` <CALCETrVz1ADNxeLzPmeWXPU5ApfKURH2vnged2A2Vng8-hUxcw@mail.gmail.com>
2011-12-28 22:45 ` Arun Sharma
2011-12-28 23:42 ` Andy Lutomirski
2011-12-29 0:19 ` Arun Sharma
2011-12-25 16:51 ` [PATCH 2/4] x86-64: Add __vdso_clock_gettime_ns vsyscall Andy Lutomirski
2011-12-25 16:51 ` [PATCH 3/4] x86-64: Optimize vdso clock_gettime Andy Lutomirski
2011-12-25 16:51 ` [PATCH 4/4] x86-64: Inline vdso clock_gettime helpers Andy Lutomirski
2011-12-27 7:46 ` [PATCH 0/4] clock_gettime_ns and x86-64 optimizations Richard Cochran
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