From: "H. Peter Anvin" <hpa@zytor.com>
To: Linus Torvalds <torvalds@linux-foundation.org>,
Denys Vlasenko <dvlasenk@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Borislav Petkov <bp@alien8.de>,
Andy Lutomirski <luto@amacapital.net>,
Oleg Nesterov <oleg@redhat.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Alexei Starovoitov <ast@plumgrid.com>,
Will Drewry <wad@chromium.org>, Kees Cook <keescook@chromium.org>,
the arch/x86 maintainers <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86/asm/entry/64: pack interrupt dispatch table tighter
Date: Fri, 03 Apr 2015 11:35:42 -0700 [thread overview]
Message-ID: <551EDD7E.3050505@zytor.com> (raw)
In-Reply-To: <CA+55aFxHSCUmsWZR4ey_NfZep-h5oyEoUL15GamQt9v17znyvQ@mail.gmail.com>
On 04/03/2015 11:08 AM, Linus Torvalds wrote:
> On Fri, Apr 3, 2015 at 9:54 AM, Denys Vlasenko <dvlasenk@redhat.com> wrote:
>>
>> How about this version?
>> It's still isn't a star of readability,
>> but the structure of the 32-byte code block is more visible now...
>
> Do we really even want to be this clever in the first place?
>
> The thing is, when we take an interrupt:
>
> (a) the L1 I$ is always cold
>
> (b) the instruction decoder has never had time to run ahead
>
> (c) there are usually not that many different interrupts anyway, even
> under load (ie you'd have maybe disk and networking)
>
> (d) we intentionally spread out the different interrupt vector numbers
>
> (e) the 32-byte block thing is questionable, most older
> micro-architectures fetch in 16-byte blocks iirc.
>
For the record, I actually measured the impact of the jump-to-jump when
I wrote it. It has a small, *but measurable*, positive impact.
-hpa
next prev parent reply other threads:[~2015-04-03 18:36 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-03 11:13 [PATCH] x86/asm/entry/64: pack interrupt dispatch table tighter Denys Vlasenko
2015-04-03 14:03 ` Ingo Molnar
2015-04-03 16:12 ` Denys Vlasenko
2015-04-03 16:54 ` Denys Vlasenko
2015-04-03 18:08 ` Linus Torvalds
2015-04-03 18:35 ` H. Peter Anvin [this message]
2015-04-03 18:37 ` Linus Torvalds
2015-04-03 19:06 ` H. Peter Anvin
2015-04-04 6:42 ` Ingo Molnar
2015-04-03 18:36 ` Denys Vlasenko
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