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

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Message-Id: <20161122081925.GB3612@linux.vnet.ibm.com>
Date:   Tue, 22 Nov 2016 00:19:25 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Olsa <jolsa@...hat.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!

On Mon, Nov 21, 2016 at 12:44:45PM -0800, Andi Kleen wrote:
> > > 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

Hmmm...  It does indeed look like some performance analysis would be good...

							Thanx, Paul