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Date:   Wed, 2 Oct 2019 20:21:06 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Daniel Bristot de Oliveira <bristot@redhat.com>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        Nadav Amit <nadav.amit@gmail.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Song Liu <songliubraving@fb.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 3/3] x86/ftrace: Use text_poke()
Message-ID: <20191002182106.GC4643@worktop.programming.kicks-ass.net>
References: <20190827180622.159326993@infradead.org>
 <20190827181147.166658077@infradead.org>
 <aaffb32f-6ca9-f9e3-9b1a-627125c563ed@redhat.com>
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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.