From: Rik van Riel <riel@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 1/2] x86/entry: Avoid interrupt flag save and restore
Date: Mon, 20 Jun 2016 16:21:55 -0400 [thread overview]
Message-ID: <1466454115.2756.45.camel@redhat.com> (raw)
In-Reply-To: <1466434712-31440-2-git-send-email-pbonzini@redhat.com>
[-- Attachment #1: Type: text/plain, Size: 1701 bytes --]
On Mon, 2016-06-20 at 16:58 +0200, Paolo Bonzini wrote:
> Thanks to all the work that was done by Andy Lutomirski and others,
> enter_from_user_mode and prepare_exit_to_usermode are now called only
> with
> interrupts disabled. Let's provide them a version of
> user_enter/user_exit
> that skips saving and restoring the interrupt flag.
>
> On an AMD-based machine I tested this patch on, with force-enabled
> context tracking, the speed-up in system calls was 90 clock cycles or
> 6%,
> measured with the following simple benchmark:
>
> #include <sys/signal.h>
> #include <time.h>
> #include <unistd.h>
> #include <stdio.h>
>
> unsigned long rdtsc()
> {
> unsigned long result;
> asm volatile("rdtsc; shl $32, %%rdx; mov %%eax, %%eax\n"
> "or %%rdx, %%rax" : "=a" (result) : : "rdx");
> return result;
> }
>
> int main()
> {
> unsigned long tsc1, tsc2;
> int pid = getpid();
> int i;
>
> tsc1 = rdtsc();
> for (i = 0; i < 100000000; i++)
> kill(pid, SIGWINCH);
> tsc2 = rdtsc();
>
> printf("%ld\n", tsc2 - tsc1);
> }
>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>
Reviewed-by: Rik van Riel <riel@redhat.com>
--
All Rights Reversed.
[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 473 bytes --]
next prev parent reply other threads:[~2016-06-20 20:24 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-20 14:58 [PATCH v2 0/2] x86/entry: speed up context-tracking system calls by 150 clock cycles Paolo Bonzini
2016-06-20 14:58 ` [PATCH 1/2] x86/entry: Avoid interrupt flag save and restore Paolo Bonzini
2016-06-20 20:21 ` Rik van Riel [this message]
2016-06-20 20:34 ` Andy Lutomirski
2016-07-09 11:52 ` [tip:x86/asm] " tip-bot for Paolo Bonzini
2016-07-10 11:37 ` tip-bot for Paolo Bonzini
2016-06-20 14:58 ` [PATCH 2/2] x86/entry: Inline enter_from_user_mode Paolo Bonzini
2016-06-20 20:22 ` Rik van Riel
2016-07-09 11:53 ` [tip:x86/asm] x86/entry: Inline enter_from_user_mode() tip-bot for Paolo Bonzini
2016-07-09 13:38 ` Borislav Petkov
2016-07-10 11:33 ` Ingo Molnar
2016-07-10 11:38 ` tip-bot for Paolo Bonzini
2016-06-20 14:58 ` [PATCH 3/2] context_tracking: move rcu_virt_note_context_switch out of kvm_host.h Paolo Bonzini
2016-06-20 20:23 ` Rik van Riel
2016-06-20 14:58 ` [PATCH 4/2] KVM: remove kvm_guest_enter/exit wrappers Paolo Bonzini
2016-06-20 20:24 ` Rik van Riel
2016-06-21 13:24 ` [PATCH v2 0/2] x86/entry: speed up context-tracking system calls by 150 clock cycles Christian Borntraeger
2016-06-21 13:26 ` Paolo Bonzini
2016-06-28 12:16 ` Paolo Bonzini
2016-07-06 13:47 ` Paolo Bonzini
-- strict thread matches above, loose matches on Subject: below --
2016-05-30 12:30 [PATCH " Paolo Bonzini
2016-05-30 12:30 ` [PATCH 1/2] x86/entry: Avoid interrupt flag save and restore Paolo Bonzini
2016-06-01 14:52 ` Rik van Riel
2016-06-04 5:07 ` Andy Lutomirski
2016-06-06 15:47 ` Paolo Bonzini
2016-06-08 12:16 ` Ingo Molnar
2016-06-08 12:34 ` Paolo Bonzini
2016-06-08 12:54 ` Ingo Molnar
2016-06-08 13:39 ` Paolo Bonzini
2016-06-08 13:46 ` 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=1466454115.2756.45.camel@redhat.com \
--to=riel@redhat.com \
--cc=hpa@zytor.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=mingo@kernel.org \
--cc=pbonzini@redhat.com \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
/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).