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From: Thomas Gleixner <tglx@linutronix.de>
To: Andy Lutomirski <luto@kernel.org>
Cc: X86 ML <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Borislav Petkov <bp@alien8.de>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mgorman@suse.de>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Nadav Amit <nadav.amit@gmail.com>, Rik van Riel <riel@redhat.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Arjan van de Ven <arjan@linux.intel.com>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v3 11/11] x86/mm: Try to preserve old TLB entries using PCID
Date: Fri, 23 Jun 2017 09:29:35 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.20.1706230929260.2647@nanos> (raw)
In-Reply-To: <CALCETrU5VfJMOENEff8HCVn3mihtC_e3xN7wotSimnJujR5YeA@mail.gmail.com>

On Thu, 22 Jun 2017, Andy Lutomirski wrote:
> On Thu, Jun 22, 2017 at 2:22 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> > On Thu, 22 Jun 2017, Andy Lutomirski wrote:
> >> On Thu, Jun 22, 2017 at 5:21 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> >> > Now one other optimization which should be trivial to add is to keep the 4
> >> > asid context entries in cpu_tlbstate and cache the last asid in thread
> >> > info. If that's still valid then use it otherwise unconditionally get a new
> >> > one. That avoids the whole loop machinery and thread info is cache hot in
> >> > the context switch anyway. Delta patch on top of your version below.
> >>
> >> I'm not sure I understand.  If an mm has ASID 0 on CPU 0 and ASID 1 on
> >> CPU 1 and a thread in that mm bounces back and forth between those
> >> CPUs, won't your patch cause it to flush every time?
> >
> > Yeah, I was too focussed on the non migratory case, where two tasks from
> > different processes play rapid ping pong. That's what I was looking at for
> > various reasons.
> >
> > There the cached asid really helps by avoiding the loop completely, but
> > yes, the search needs to be done for the bouncing between CPUs case.
> >
> > So maybe a combo of those might be interesting.
> >
> 
> I'm not too worried about optimizing away the loop.  It's a loop over
> four or six things that are all in cachelines that we need anyway.  I
> suspect that we'll never be able to see it in any microbenchmark, let
> alone real application.

Fair enough.

  reply	other threads:[~2017-06-23  7:29 UTC|newest]

Thread overview: 78+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-06-21  5:22 [PATCH v3 00/11] PCID and improved laziness Andy Lutomirski
2017-06-21  5:22 ` [PATCH v3 01/11] x86/mm: Don't reenter flush_tlb_func_common() Andy Lutomirski
2017-06-21  8:01   ` Thomas Gleixner
2017-06-21  8:49   ` Borislav Petkov
2017-06-21 15:15     ` Andy Lutomirski
2017-06-21 23:26   ` Nadav Amit
2017-06-22  2:27     ` Andy Lutomirski
2017-06-22  7:32       ` Ingo Molnar
2017-06-21  5:22 ` [PATCH v3 02/11] x86/ldt: Simplify LDT switching logic Andy Lutomirski
2017-06-21  8:03   ` Thomas Gleixner
2017-06-21  9:40   ` Borislav Petkov
2017-06-22 11:08   ` [tip:x86/mm] x86/ldt: Simplify the " tip-bot for Andy Lutomirski
2017-06-21  5:22 ` [PATCH v3 03/11] x86/mm: Remove reset_lazy_tlbstate() Andy Lutomirski
2017-06-21  8:03   ` Thomas Gleixner
2017-06-21  9:50   ` Borislav Petkov
2017-06-22 11:08   ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2017-06-21  5:22 ` [PATCH v3 04/11] x86/mm: Give each mm TLB flush generation a unique ID Andy Lutomirski
2017-06-21  8:05   ` Thomas Gleixner
2017-06-21 10:33   ` Borislav Petkov
2017-06-21 15:23     ` Andy Lutomirski
2017-06-21 17:06       ` Borislav Petkov
2017-06-21 17:43   ` Borislav Petkov
2017-06-22  2:34     ` Andy Lutomirski
2017-06-21  5:22 ` [PATCH v3 05/11] x86/mm: Track the TLB's tlb_gen and update the flushing algorithm Andy Lutomirski
2017-06-21  8:32   ` Thomas Gleixner
2017-06-21 15:11     ` Andy Lutomirski
2017-06-21 18:44   ` Borislav Petkov
2017-06-22  2:46     ` Andy Lutomirski
2017-06-22  7:24       ` Borislav Petkov
2017-06-22 14:48         ` Andy Lutomirski
2017-06-22 14:59           ` Borislav Petkov
2017-06-22 15:55             ` Andy Lutomirski
2017-06-22 17:22               ` Borislav Petkov
2017-06-22 18:08                 ` Andy Lutomirski
2017-06-23  8:42                   ` Borislav Petkov
2017-06-23 15:46                     ` Andy Lutomirski
2017-06-21  5:22 ` [PATCH v3 06/11] x86/mm: Rework lazy TLB mode and TLB freshness tracking Andy Lutomirski
2017-06-21  9:01   ` Thomas Gleixner
2017-06-21 16:04     ` Andy Lutomirski
2017-06-21 17:29       ` Borislav Petkov
2017-06-22 14:50   ` Borislav Petkov
2017-06-22 17:47     ` Andy Lutomirski
2017-06-22 19:05       ` Borislav Petkov
2017-07-27 19:53       ` Andrew Banman
2017-07-28  2:05         ` Andy Lutomirski
2017-06-23 13:34   ` Boris Ostrovsky
2017-06-23 15:22     ` Andy Lutomirski
2017-06-21  5:22 ` [PATCH v3 07/11] x86/mm: Stop calling leave_mm() in idle code Andy Lutomirski
2017-06-21  9:22   ` Thomas Gleixner
2017-06-21 15:16     ` Andy Lutomirski
2017-06-23  9:07   ` Borislav Petkov
2017-06-21  5:22 ` [PATCH v3 08/11] x86/mm: Disable PCID on 32-bit kernels Andy Lutomirski
2017-06-21  9:26   ` Thomas Gleixner
2017-06-23  9:24   ` Borislav Petkov
2017-06-21  5:22 ` [PATCH v3 09/11] x86/mm: Add nopcid to turn off PCID Andy Lutomirski
2017-06-21  9:27   ` Thomas Gleixner
2017-06-23  9:34   ` Borislav Petkov
2017-06-21  5:22 ` [PATCH v3 10/11] x86/mm: Enable CR4.PCIDE on supported systems Andy Lutomirski
2017-06-21  9:39   ` Thomas Gleixner
2017-06-21 13:40     ` Thomas Gleixner
2017-06-21 20:34     ` Andy Lutomirski
2017-06-23 11:50   ` Borislav Petkov
2017-06-23 15:28     ` Andy Lutomirski
2017-06-23 13:35   ` Boris Ostrovsky
2017-06-21  5:22 ` [PATCH v3 11/11] x86/mm: Try to preserve old TLB entries using PCID Andy Lutomirski
2017-06-21 13:38   ` Thomas Gleixner
2017-06-21 13:40     ` Thomas Gleixner
2017-06-22  2:57     ` Andy Lutomirski
2017-06-22 12:21       ` Thomas Gleixner
2017-06-22 18:12         ` Andy Lutomirski
2017-06-22 21:22           ` Thomas Gleixner
2017-06-23  3:09             ` Andy Lutomirski
2017-06-23  7:29               ` Thomas Gleixner [this message]
2017-06-22 16:09   ` Nadav Amit
2017-06-22 18:10     ` Andy Lutomirski
2017-06-26 15:58   ` Borislav Petkov
2017-06-21 18:23 ` [PATCH v3 00/11] PCID and improved laziness Linus Torvalds
2017-06-22  5:19   ` Andy Lutomirski

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