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From: Arun Sharma <asharma@fb.com>
To: John Stultz <john.stultz@linaro.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Kumar Sundararajan <kumar@fb.com>,
	Richard Cochran <richardcochran@gmail.com>,
	"H. Peter Anvin" <hpa@linux.intel.com>
Subject: Re: clock_gettime_ns
Date: Thu, 5 Sep 2013 10:15:39 +0530	[thread overview]
Message-ID: <52280C73.9080209@fb.com> (raw)
In-Reply-To: <CANcMJZAv_-nGkjt8r8cp+BhnSfhL2roKZpodN+vLKfmpTVLhrQ@mail.gmail.com>

On 9/5/13 12:47 AM, John Stultz wrote:
> If we're going to add a new interface that uses something other then a
> timespec, we likely need to put some serious thought into that new
> type, and see how it could be used across a number of syscalls. Some
> of the discussion around dealing with the 2038 issue touched on this.

[ I know you're not asking for perf data, but may be useful for new 
readers ]

Here's the benchmarking I did in 2011:

http://thread.gmane.org/gmane.linux.kernel/1233758/focus=1233781

Switching from timespec to s64 was worth 21%. My experience over the 
years is that this performance delta causes userspace guys to implement 
their own TSC based timers, against the advice from kernel developers.

http://code.ohloh.net/search?s=wall%20now%20tsc%20hz&pp=0&fl=C&fl=C%2B%2B&ff=1&mp=1&ml=1&me=1&md=1&filterChecked=true

I worry that trying to solve other clock problems will cause the kernel 
to continue to pass the time in memory instead of registers, giving the 
userspace TSC based implementations a reason to exist.

  -Arun

      parent reply	other threads:[~2013-09-05  5:12 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-09-04  9:18 clock_gettime_ns Arun Sharma
2013-09-04 18:51 ` clock_gettime_ns Andy Lutomirski
2013-09-04 19:20   ` clock_gettime_ns John Stultz
2013-09-04 20:33     ` clock_gettime_ns Andy Lutomirski
2013-09-04 20:54       ` clock_gettime_ns John Stultz
2013-09-04 22:29         ` clock_gettime_ns H. Peter Anvin
2013-09-04 22:59           ` clock_gettime_ns John Stultz
2013-09-04 23:04             ` clock_gettime_ns H. Peter Anvin
2013-09-04 23:20               ` clock_gettime_ns John Stultz
2013-09-04 23:38           ` clock_gettime_ns Andy Lutomirski
2013-09-05  1:22             ` clock_gettime_ns H. Peter Anvin
2013-09-09 17:47               ` clock_gettime_ns Andy Lutomirski
2013-09-11 18:50                 ` clock_gettime_ns Richard Cochran
2013-09-04 19:17 ` clock_gettime_ns John Stultz
2013-09-04 20:23   ` clock_gettime_ns Andy Lutomirski
2013-09-04 20:50     ` clock_gettime_ns John Stultz
2013-09-05  4:45   ` Arun Sharma [this message]

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