linux-kernel - Re: [PATCH 3/3] x86/ftrace: Use text

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Message-ID: <20191002182106.GC4643@worktop.programming.kicks-ass.net>
Date:   Wed, 2 Oct 2019 20:21:06 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Nadav Amit <nadav.amit@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Song Liu <songliubraving@...com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 3/3] x86/ftrace: Use text_poke()

On Wed, Oct 02, 2019 at 06:35:26PM +0200, Daniel Bristot de Oliveira wrote:

> ftrace was already batching the updates, for instance, causing 3 IPIs to enable
> all functions. The text_poke() batching also works. But because of the limited
> buffer [ see the reply to the patch 2/3 ], it is flushing the buffer during the
> operation, causing more IPIs than the previous code. Using the 5.4-rc1 in a VM,
> when enabling the function tracer, I see 250+ intermediate text_poke_finish()
> because of a full buffer...
> 
> Would this be the case of trying to use a dynamically allocated buffer?
> 
> Thoughts?

Is it a problem? I tried growing the buffer (IIRC I made it 10 times
bigger) and didn't see any performance improvements because of it.