linux-kernel - Re: [BUG] msr-trace.h:42 suspicious rcu_dereference

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Message-ID: <20161121204445.GX26852@two.firstfloor.org>
Date:   Mon, 21 Nov 2016 12:44:45 -0800
From:   Andi Kleen <andi@...stfloor.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Andi Kleen <andi@...stfloor.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Olsa <jolsa@...hat.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Jan Stancek <jstancek@...hat.com>
Subject: Re: [BUG] msr-trace.h:42 suspicious rcu_dereference_check() usage!

> > http://halobates.de/tracepoint-trace
> 
> There's a lot of push and pop regs due to function calling. There's
> places that inlines can still improve things, and perhaps even some
> likely unlikelys well placed.

Assuming you avoid all the push/pop and all the call/ret this would only be
~25% of the total instructions. There is just far too much logic and
computation in there.

% awk ' { print $5 } '  tracepoint-trace | sort | uniq -c | sort -rn
    222 mov
     57 push
     57 pop
     35 test
     34 cmp
     32 and
     28 jz
     25 jnz
     21 ret
     20 call
     16 lea
     11 add

-Andi