From: Andy Lutomirski <luto@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>, 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>
Subject: Re: [PATCH v4 10/10] x86/mm: Try to preserve old TLB entries using PCID
Date: Wed, 5 Jul 2017 09:10:00 -0700 [thread overview]
Message-ID: <CALCETrXYQHQm2qQ_4dLx8K2rFfapFUb-eqFdG8bk2377eFnNGg@mail.gmail.com> (raw)
In-Reply-To: <20170705122506.GG4941@worktop>
On Wed, Jul 5, 2017 at 5:25 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, Jun 29, 2017 at 08:53:22AM -0700, Andy Lutomirski wrote:
>> +static void choose_new_asid(struct mm_struct *next, u64 next_tlb_gen,
>> + u16 *new_asid, bool *need_flush)
>> +{
>> + u16 asid;
>> +
>> + if (!static_cpu_has(X86_FEATURE_PCID)) {
>> + *new_asid = 0;
>> + *need_flush = true;
>> + return;
>> + }
>> +
>> + for (asid = 0; asid < TLB_NR_DYN_ASIDS; asid++) {
>> + if (this_cpu_read(cpu_tlbstate.ctxs[asid].ctx_id) !=
>> + next->context.ctx_id)
>> + continue;
>> +
>> + *new_asid = asid;
>> + *need_flush = (this_cpu_read(cpu_tlbstate.ctxs[asid].tlb_gen) <
>> + next_tlb_gen);
>> + return;
>> + }
>> +
>> + /*
>> + * We don't currently own an ASID slot on this CPU.
>> + * Allocate a slot.
>> + */
>> + *new_asid = this_cpu_add_return(cpu_tlbstate.next_asid, 1) - 1;
>
> So this basically RR the ASID slots. Have you tried slightly more
> complex replacement policies like CLOCK ?
No, mainly because I'm lazy and because CLOCK requires scavenging a
bit. (Which we can certainly do, but it will further complicate the
code.) It could be worth playing with better replacement algorithms
as a followup, though.
I've also considered a slight elaboration of RR in which we make sure
not to reuse the most recent ASID slot, which would guarantee that, if
we switch from task A to B and back to A, we don't flush on the way
back to A. (Currently, if B is not in the cache, there's a 1/6 chance
we'll flush on the way back.)
next prev parent reply other threads:[~2017-07-05 16:10 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-29 15:53 [PATCH v4 00/10] PCID and improved laziness Andy Lutomirski
2017-06-29 15:53 ` [PATCH v4 01/10] x86/mm: Don't reenter flush_tlb_func_common() Andy Lutomirski
2017-06-30 13:11 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2017-06-29 15:53 ` [PATCH v4 02/10] x86/mm: Delete a big outdated comment about TLB flushing Andy Lutomirski
2017-06-30 13:11 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2017-06-29 15:53 ` [PATCH v4 03/10] x86/mm: Give each mm TLB flush generation a unique ID Andy Lutomirski
2017-07-05 10:31 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2017-07-05 10:58 ` Peter Zijlstra
2017-06-29 15:53 ` [PATCH v4 04/10] x86/mm: Track the TLB's tlb_gen and update the flushing algorithm Andy Lutomirski
2017-07-05 10:31 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2017-06-29 15:53 ` [PATCH v4 05/10] x86/mm: Rework lazy TLB mode and TLB freshness tracking Andy Lutomirski
2017-07-05 10:31 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2017-06-29 15:53 ` [PATCH v4 06/10] x86/mm: Stop calling leave_mm() in idle code Andy Lutomirski
2017-07-05 10:32 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2017-06-29 15:53 ` [PATCH v4 07/10] x86/mm: Disable PCID on 32-bit kernels Andy Lutomirski
2017-07-05 10:32 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2017-06-29 15:53 ` [PATCH v4 08/10] x86/mm: Add nopcid to turn off PCID Andy Lutomirski
2017-07-05 10:32 ` [tip:x86/mm] x86/mm: Add the 'nopcid' boot option " tip-bot for Andy Lutomirski
2017-06-29 15:53 ` [PATCH v4 09/10] x86/mm: Enable CR4.PCIDE on supported systems Andy Lutomirski
2017-07-05 10:33 ` [tip:x86/mm] " tip-bot for Andy Lutomirski
2017-06-29 15:53 ` [PATCH v4 10/10] x86/mm: Try to preserve old TLB entries using PCID Andy Lutomirski
2017-07-03 10:56 ` Thomas Gleixner
2017-07-05 12:18 ` Peter Zijlstra
2017-07-05 16:04 ` Andy Lutomirski
2017-07-05 17:02 ` Peter Zijlstra
2017-07-18 8:53 ` Ingo Molnar
2017-07-18 17:06 ` Andy Lutomirski
2017-07-05 12:25 ` Peter Zijlstra
2017-07-05 16:10 ` Andy Lutomirski [this message]
2017-07-28 13:49 ` Peter Zijlstra
2017-06-30 12:44 ` [PATCH v4 00/10] PCID and improved laziness Matt Fleming
2017-07-11 11:32 ` Matt Fleming
2017-07-11 15:00 ` Andy Lutomirski
2017-07-13 19:36 ` Matt Fleming
2017-07-05 8:56 ` Ingo Molnar
2017-07-05 16:53 ` Linus Torvalds
2017-07-17 9:57 ` Mel Gorman
2017-07-17 15:06 ` Ingo Molnar
2017-07-17 15:56 ` Mel Gorman
[not found] ` <CALBSrqDW6pGjHxOmzfnkY_KoNeH6F=pTb8-tJ8r-zbu4prw9HQ@mail.gmail.com>
2017-09-12 19:32 ` Sai Praneeth Prakhya
2017-09-13 4:14 ` Sai Praneeth Prakhya
[not found] ` <428E07CE-6F76-4137-B568-B9794735A51F@amacapital.net>
2017-09-13 7:43 ` Ingo Molnar
2017-09-13 7:45 ` Ingo Molnar
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CALCETrXYQHQm2qQ_4dLx8K2rFfapFUb-eqFdG8bk2377eFnNGg@mail.gmail.com \
--to=luto@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=arjan@linux.intel.com \
--cc=bp@alien8.de \
--cc=dave.hansen@intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mgorman@suse.de \
--cc=nadav.amit@gmail.com \
--cc=peterz@infradead.org \
--cc=riel@redhat.com \
--cc=torvalds@linux-foundation.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).