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Date: Tue, 25 Nov 2014 10:25:43 -0500 From: Rik van Riel <riel@...hat.com> To: Khalid Aziz <khalid.aziz@...cle.com>, tglx@...utronix.de, corbet@....net, mingo@...hat.com, hpa@...or.com, peterz@...radead.org, akpm@...ux-foundation.org, rientjes@...gle.com, ak@...ux.intel.com, mgorman@...e.de, liwanp@...ux.vnet.ibm.com, raistlin@...ux.it, kirill.shutemov@...ux.intel.com, atomlin@...hat.com, avagin@...nvz.org, gorcunov@...nvz.org, serge.hallyn@...onical.com, athorlton@....com, oleg@...hat.com, vdavydov@...allels.com, daeseok.youn@...il.com, keescook@...omium.org, yangds.fnst@...fujitsu.com, sbauer@....utah.edu, vishnu.ps@...sung.com, axboe@...com, paulmck@...ux.vnet.ibm.com CC: linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org, linux-api@...r.kernel.org Subject: Re: [PATCH v3] sched/fair: Add advisory flag for borrowing a timeslice On 11/25/2014 09:52 AM, Khalid Aziz wrote: > On 11/24/2014 07:03 PM, Rik van Riel wrote: >> -----BEGIN PGP SIGNED MESSAGE----- >> Hash: SHA1 >> >> 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. > > This solution indeed is for userspace spinlocks. Database code has been > written with all critical locking implemented in userspace (as I have > been told by database folks. I am not a database guy). They should fix that. The scheme you propose can really only work on bare metal, and not on virtual machines. That improves the problem for, what, 60% of new installs (and dropping)? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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