linux-kernel - Re: [PATCH] Add a text

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Date:	Wed, 27 Nov 2013 18:10:22 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Andy Lutomirski <luto@...capital.net>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] Add a text_poke syscall v2

ftrace is the flagship example.

And yes, agreed about timeouts.

Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>On Wed, Nov 27, 2013 at 3:28 PM, H. Peter Anvin <hpa@...or.com> wrote:
>>
>> The timeout bit was an acknowledgment that some kind of batching
>> interface is necessary.
>
>That's just moronic. People would make up totally random timeouts, so
>from an interface standpoint it's just horrid, horrid.
>
>Giving user space random knobs that you don't understand yourself, and
>the monkeys in user space are guaranteed to mis-use is just entirely
>the wrong thing to do.
>
>Much better to then just making the interface itself be about
>batching, which isn't as hard as you make it out to be. Make it an
>array of those addr/replace/len things. And we have that
>"restart_block" for system calls, and we'd limit batching to some
>random smallish number ("128 instructions, just because"), while still
>being easily interruptible in between those blocks. That limits you to
>two IPI's per 128 instructions replaced - and at that point even
>*that* is just an internal kernel random tuning thing, not some insane
>user interface.
>
>But is such batching really even worth it? If' it's not *that* much
>more effort, maybe it's worth it, but do we have known users that
>really would have thousands and thousands of cases all at once?
>
>            Linus

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