* Re: [tip:x86/mm] x86/mm: Avoid superflous leave_mm() in the TLB flush path [not found] <tip-287de5b2cb365b98190b5de8ace1c5a31768a5ae@git.kernel.org> @ 2011-12-05 23:26 ` Linus Torvalds 2011-12-06 0:40 ` Shaohua Li 0 siblings, 1 reply; 3+ messages in thread From: Linus Torvalds @ 2011-12-05 23:26 UTC (permalink / raw) To: linux-kernel, mingo, hpa, torvalds, shaohua.li, akpm, tglx, mingo Cc: linux-tip-commits On Mon, Dec 5, 2011 at 9:56 AM, tip-bot for Shaohua Li <shaohua.li@intel.com> wrote: > > x86/mm: Avoid superflous leave_mm() in the TLB flush path > > If just one page VA tlb is required to be flushed and current > task is in lazy TLB state, doing leave_mm() is superfluous > because it flushes the whole TLB. This can reduce some TLB > miss. Are you sure this is a good idea? We may be *much* better off leaving the VM and avoiding future IPI's than trying to flush pages one by one over and over again. IPI's are expensive. I don't think you thought this through, and if you *did* think it through and actually have numbers that it's cheaper to stay with the MM, I think you need to show those numbers. Linus ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [tip:x86/mm] x86/mm: Avoid superflous leave_mm() in the TLB flush path 2011-12-05 23:26 ` [tip:x86/mm] x86/mm: Avoid superflous leave_mm() in the TLB flush path Linus Torvalds @ 2011-12-06 0:40 ` Shaohua Li 2011-12-06 5:31 ` Ingo Molnar 0 siblings, 1 reply; 3+ messages in thread From: Shaohua Li @ 2011-12-06 0:40 UTC (permalink / raw) To: Linus Torvalds Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, hpa@zytor.com, akpm@linux-foundation.org, tglx@linutronix.de, mingo@elte.hu, linux-tip-commits@vger.kernel.org On Tue, 2011-12-06 at 07:26 +0800, Linus Torvalds wrote: > On Mon, Dec 5, 2011 at 9:56 AM, tip-bot for Shaohua Li > <shaohua.li@intel.com> wrote: > > > > x86/mm: Avoid superflous leave_mm() in the TLB flush path > > > > If just one page VA tlb is required to be flushed and current > > task is in lazy TLB state, doing leave_mm() is superfluous > > because it flushes the whole TLB. This can reduce some TLB > > miss. > > Are you sure this is a good idea? > > We may be *much* better off leaving the VM and avoiding future IPI's > than trying to flush pages one by one over and over again. > > IPI's are expensive. > > I don't think you thought this through, and if you *did* think it > through and actually have numbers that it's cheaper to stay with the > MM, I think you need to show those numbers. good point, I didn't think of it. It's unlikely we just flush one tlb page. please drop the patch. Thanks, Shaohua ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [tip:x86/mm] x86/mm: Avoid superflous leave_mm() in the TLB flush path 2011-12-06 0:40 ` Shaohua Li @ 2011-12-06 5:31 ` Ingo Molnar 0 siblings, 0 replies; 3+ messages in thread From: Ingo Molnar @ 2011-12-06 5:31 UTC (permalink / raw) To: Shaohua Li Cc: Linus Torvalds, linux-kernel@vger.kernel.org, mingo@redhat.com, hpa@zytor.com, akpm@linux-foundation.org, tglx@linutronix.de, linux-tip-commits@vger.kernel.org * Shaohua Li <shaohua.li@intel.com> wrote: > On Tue, 2011-12-06 at 07:26 +0800, Linus Torvalds wrote: > > On Mon, Dec 5, 2011 at 9:56 AM, tip-bot for Shaohua Li > > <shaohua.li@intel.com> wrote: > > > > > > x86/mm: Avoid superflous leave_mm() in the TLB flush path > > > > > > If just one page VA tlb is required to be flushed and current > > > task is in lazy TLB state, doing leave_mm() is superfluous > > > because it flushes the whole TLB. This can reduce some TLB > > > miss. > > > > Are you sure this is a good idea? > > > > We may be *much* better off leaving the VM and avoiding future IPI's > > than trying to flush pages one by one over and over again. > > > > IPI's are expensive. > > > > I don't think you thought this through, and if you *did* think it > > through and actually have numbers that it's cheaper to stay with the > > MM, I think you need to show those numbers. > > good point, I didn't think of it. It's unlikely we just flush > one tlb page. please drop the patch. Dropped, thanks guys. Ingo ^ permalink raw reply [flat|nested] 3+ messages in thread
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[not found] <tip-287de5b2cb365b98190b5de8ace1c5a31768a5ae@git.kernel.org>
2011-12-05 23:26 ` [tip:x86/mm] x86/mm: Avoid superflous leave_mm() in the TLB flush path Linus Torvalds
2011-12-06 0:40 ` Shaohua Li
2011-12-06 5:31 ` Ingo Molnar
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