From: Borislav Petkov <bp@alien8.de>
To: Andy Lutomirski <luto@kernel.org>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
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: Mon, 26 Jun 2017 17:58:29 +0200 [thread overview]
Message-ID: <20170626155829.4t2axppz7gwf7trd@pd.tnic> (raw)
In-Reply-To: <a8cdfbbb17785aed10980d24692745f68615a584.1498022414.git.luto@kernel.org>
On Tue, Jun 20, 2017 at 10:22:17PM -0700, Andy Lutomirski wrote:
> PCID is a "process context ID" -- it's what other architectures call
> an address space ID. Every non-global TLB entry is tagged with a
> PCID, only TLB entries that match the currently selected PCID are
> used, and we can switch PGDs without flushing the TLB. x86's
> PCID is 12 bits.
>
> This is an unorthodox approach to using PCID. x86's PCID is far too
> short to uniquely identify a process, and we can't even really
> uniquely identify a running process because there are monster
> systems with over 4096 CPUs. To make matters worse, past attempts
> to use all 12 PCID bits have resulted in slowdowns instead of
> speedups.
>
> This patch uses PCID differently. We use a PCID to identify a
> recently-used mm on a per-cpu basis. An mm has no fixed PCID
> binding at all; instead, we give it a fresh PCID each time it's
> loaded except in cases where we want to preserve the TLB, in which
> case we reuse a recent value.
>
> This seems to save about 100ns on context switches between mms.
"... with my microbenchmark of ping-ponging." :)
>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
> arch/x86/include/asm/mmu_context.h | 3 ++
> arch/x86/include/asm/processor-flags.h | 2 +
> arch/x86/include/asm/tlbflush.h | 18 +++++++-
> arch/x86/mm/init.c | 1 +
> arch/x86/mm/tlb.c | 82 ++++++++++++++++++++++++++--------
> 5 files changed, 86 insertions(+), 20 deletions(-)
...
> diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
> index 57b305e13c4c..a9a5aa6f45f7 100644
> --- a/arch/x86/include/asm/tlbflush.h
> +++ b/arch/x86/include/asm/tlbflush.h
> @@ -82,6 +82,12 @@ static inline u64 bump_mm_tlb_gen(struct mm_struct *mm)
> #define __flush_tlb_single(addr) __native_flush_tlb_single(addr)
> #endif
>
> +/*
> + * 6 because 6 should be plenty and struct tlb_state will fit in
> + * two cache lines.
> + */
> +#define NR_DYNAMIC_ASIDS 6
TLB_NR_DYN_ASIDS
Properly prefixed, I guess.
The rest later, when you're done experimenting. :)
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
next prev parent reply other threads:[~2017-06-26 15:59 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
2017-06-22 16:09 ` Nadav Amit
2017-06-22 18:10 ` Andy Lutomirski
2017-06-26 15:58 ` Borislav Petkov [this message]
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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