From: Peter Zijlstra <peterz@infradead.org>
To: Rik van Riel <riel@redhat.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
corbet@lwn.net, mingo@redhat.com, hpa@zytor.com,
akpm@linux-foundation.org, rientjes@google.com,
ak@linux.intel.com, mgorman@suse.de, raistlin@linux.it,
kirill.shutemov@linux.intel.com, atomlin@redhat.com,
avagin@openvz.org, gorcunov@openvz.org,
serge.hallyn@canonical.com, athorlton@sgi.com, oleg@redhat.com,
vdavydov@parallels.com, daeseok.youn@gmail.com,
keescook@chromium.org, yangds.fnst@cn.fujitsu.com,
sbauer@eng.utah.edu, vishnu.ps@samsung.com, axboe@fb.com,
paulmck@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
linux-doc@vger.kernel.org, linux-api@vger.kernel.org
Subject: Re: [PATCH RESEND v4] sched/fair: Add advisory flag for borrowing a timeslice
Date: Tue, 13 Jan 2015 12:25:16 +0100 [thread overview]
Message-ID: <20150113112516.GH25256@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <5499B8A2.4080008@redhat.com>
On Tue, Dec 23, 2014 at 01:46:58PM -0500, Rik van Riel wrote:
> An uncontended futex is taken without ever going into kernel
> space. Adaptive spinning allows short duration futexes to be
> taken without going into kernel space.
The going into kernel is a red herring afaict, a no-op syscall costs ~180
cycles or something like that. So sure you can do a wee spin (~90 cycles
to try and amortize that), but I really doubt that this is the problem.
prev parent reply other threads:[~2015-01-13 11:25 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-18 18:44 Khalid Aziz
2014-12-18 22:28 ` Peter Zijlstra
2014-12-18 22:42 ` Khalid Aziz
2014-12-18 23:02 ` Thomas Gleixner
2014-12-18 23:38 ` Khalid Aziz
2014-12-19 0:27 ` Thomas Gleixner
2014-12-19 21:43 ` Khalid Aziz
2014-12-19 23:57 ` Thomas Gleixner
2014-12-22 16:40 ` Khalid Aziz
2014-12-23 10:52 ` Ingo Molnar
2014-12-23 15:13 ` Khalid Aziz
2014-12-23 18:46 ` Rik van Riel
2014-12-23 20:47 ` Khalid Aziz
2014-12-23 22:33 ` Rik van Riel
2015-01-13 11:25 ` Peter Zijlstra [this message]
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