Message-ID: <5473E388.6000605@redhat.com>
Date: Mon, 24 Nov 2014 21:03:52 -0500
From: Rik van Riel <riel@redhat.com>
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To: Khalid Aziz <khalid.aziz@oracle.com>, tglx@linutronix.de, corbet@lwn.net,
        mingo@redhat.com, hpa@zytor.com, peterz@infradead.org,
        akpm@linux-foundation.org, rientjes@google.com, ak@linux.intel.com,
        mgorman@suse.de, liwanp@linux.vnet.ibm.com, 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
CC: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-api@vger.kernel.org
Subject: Re: [PATCH v3] sched/fair: Add advisory flag for borrowing a timeslice
 (was: Pre-emption control for userspace)
References: <1416862595-24513-1-git-send-email-khalid.aziz@oracle.com>
In-Reply-To: <1416862595-24513-1-git-send-email-khalid.aziz@oracle.com>
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Sender: linux-kernel-owner@vger.kernel.org

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On 11/24/2014 03:56 PM, Khalid Aziz wrote:
> sched/fair: Add advisory flag for borrowing a timeslice
> 
> This patch adds a way for a task to request to borrow one
> timeslice from future if it is about to be preempted, so it could
> delay preemption and complete any critical task it is in the middle
> of.
> 
> This feature helps with performance on databases and has been used
> for many years on other OSs by the databases. This feature helps in
> situation where a task acquires a lock before performing a critical
> operation on the database and happens to get preempted

Why don't the other tasks that want the lock sleep on the
lock?

I can see this "solution" help mostly with userspace spinlocks,
which are relics of a past era that need to die. There is no
way userspace spinlocks will not fail miserably on virtual
machines, and it is time to get rid of them.

- -- 
All rights reversed
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