From: Andy Lutomirski <luto@amacapital.net>
To: John Stultz <john.stultz@linaro.org>
Cc: stefani@seibold.net, linux-kernel@vger.kernel.org,
ak@linux.intel.com, aarcange@redhat.com
Subject: Re: [PATCH] Add VDSO time function support for x86 32-bit kernel
Date: Tue, 11 Dec 2012 11:37:59 -0800 [thread overview]
Message-ID: <CALCETrUFsHPrzm-B=9fJac_-3b+sihWmW2sev23B4zXSh2PBqQ@mail.gmail.com> (raw)
In-Reply-To: <50C78927.6080302@linaro.org>
On Tue, Dec 11, 2012 at 11:27 AM, John Stultz <john.stultz@linaro.org> wrote:
> On 12/11/2012 08:11 AM, stefani@seibold.net wrote:
>>
>> From: Stefani Seibold <stefani@seibold.net>
>>
>> This small patch add the functions vdso_gettimeofday(),
>> vdso_clock_gettime()
>> and vdso_time() support to the VDSO for x86 32-bit kernels.
>>
>> The reason to do this was to get a fast reliable time stamp. Many
>> developers
>> uses TSC to get a fast time time stamp, without knowing the pitfalls. VDSO
>> time functions a fast and reliable way, because the kernel knows the best
>> time
>> source and the P- and C-state of the CPU.
>
> Very cool. There have been similar implementations of this patch over the
> years, but they were all bit more hackish then this.
>
>
>
>> For x86 the vclock_gettime.c currently supports only the HPET and TSC
>> timer,
>> the ACPI timer should be easily to add with an other patch.
>
> Although the ACPI PM timer requires port-io which would need tweaking to
> allow normal users to access it. And I'm not sure if the performance would
> be much improved, as the port-io probably dominates the performance cost.
>
I'd actually advocate going the other way and removing hpet vdso
support. Last time I benchmarked this, a syscall took about 20ns on
my box, and reading the hpet counter took about 750ns, giving
approximately no gain to the hpet-via-vdso optimization.
--Andy
next prev parent reply other threads:[~2012-12-11 19:38 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-11 16:11 [PATCH] Add VDSO time function support for x86 32-bit kernel stefani
2012-12-11 19:27 ` John Stultz
2012-12-11 19:37 ` Andy Lutomirski [this message]
2012-12-11 20:54 ` Stefani Seibold
2012-12-11 21:18 ` Andy Lutomirski
2012-12-11 21:28 ` Stefani Seibold
2012-12-11 19:37 ` Andy Lutomirski
2012-12-11 20:40 ` Stefani Seibold
2012-12-12 1:29 ` Andy Lutomirski
2012-12-12 20:19 stefani
2012-12-12 23:34 ` H. Peter Anvin
2012-12-13 5:53 ` Stefani Seibold
2012-12-13 6:10 ` H. Peter Anvin
2012-12-13 6:14 ` H. Peter Anvin
2012-12-13 6:17 ` Stefani Seibold
2012-12-13 6:47 ` H. Peter Anvin
2012-12-13 7:17 ` Stefani Seibold
2012-12-13 19:32 ` Andy Lutomirski
2012-12-14 0:09 ` H. Peter Anvin
2012-12-14 0:20 ` Andy Lutomirski
2012-12-14 0:36 ` H. Peter Anvin
2012-12-14 1:32 ` H. Peter Anvin
2012-12-14 1:42 ` Andy Lutomirski
2012-12-14 1:49 ` H. Peter Anvin
2012-12-14 2:11 ` Andy Lutomirski
2012-12-14 2:18 ` H. Peter Anvin
2012-12-14 2:20 ` Andy Lutomirski
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