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Date: Thu, 06 Mar 2014 09:12:42 -0700 From: Khalid Aziz <khalid.aziz@...cle.com> To: David Lang <david@...g.hm>, Kevin Easton <kevin@...rana.org> CC: Andi Kleen <andi@...stfloor.org>, Thomas Gleixner <tglx@...utronix.de>, One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>, "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>, peterz@...radead.org, akpm@...ux-foundation.org, viro@...iv.linux.org.uk, oleg@...hat.com, linux-kernel@...r.kernel.org Subject: Re: [RFC] [PATCH] Pre-emption control for userspace On 03/06/2014 07:25 AM, David Lang wrote: > On Thu, 6 Mar 2014, Kevin Easton wrote: > >> On Tue, Mar 04, 2014 at 04:51:15PM -0800, Andi Kleen wrote: >>> Anything else? >> >> If it was possible to make the time remaining in the current timeslice >> available to userspace through the vdso, the thread could do something >> like: >> >> if (sys_timeleft() < CRITICAL_SECTION_SIZE) >> yield(); >> lock(); >> >> to avoid running out of timeslice in the middle of the critical section. > > but won't the system call result in context switches? According to > Kevin, even a context switch to another thread and back immediatly is > bad enough to need to be avoided, so replacing that with the context > switch to the kernel and back isn't a subtantial win. > > David Lang Using vdso reduces the cost of system call significantly, but as Peter pointed out a thread can not really rely upon the number it will get back. -- Khalid -- 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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