linux-kernel - Re: [PATCH] x86: Align TLB invalidation info

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Message-ID: <20180201093847.GZ2269@hirez.programming.kicks-ass.net>
Date:   Thu, 1 Feb 2018 10:38:47 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nadav Amit <nadav.amit@...il.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] x86: Align TLB invalidation info

On Wed, Jan 31, 2018 at 09:38:46PM -0800, Nadav Amit wrote:

> I used ftrace to measure the execution time of flush_tlb_func_remote() on a
> 2-socket Haswell machine, using a microbenchmark I wrote for some research
> project.

However cool ftrace is, it is _really_ bad for such uses. The cost of
using ftrace is many many time higher than any change you could affect
by this.

A microbench and/or perf is what you should use for this.