linux-kernel - Re: [PATCH 4/5] Powerpc/hw-breakpoint: Optimize disable path

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Message-Id: <c4efb3e1-acb7-df2a-513d-02004d487cae@linux.ibm.com>
Date:   Wed, 19 Jun 2019 11:32:28 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
To:     Michael Neuling <mikey@...ling.org>
Cc:     mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        npiggin@...il.com, christophe.leroy@....fr,
        naveen.n.rao@...ux.vnet.ibm.com,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: Re: [PATCH 4/5] Powerpc/hw-breakpoint: Optimize disable path



On 6/18/19 11:45 AM, Michael Neuling wrote:
> On Tue, 2019-06-18 at 09:57 +0530, Ravi Bangoria wrote:
>> Directly setting dawr and dawrx with 0 should be enough to
>> disable watchpoint. No need to reset individual bits in
>> variable and then set in hw.
> 
> This seems like a pointless optimisation to me. 
> 
> I'm all for adding more code/complexity if it buys us some performance, but I
> can't imagine this is a fast path (nor have you stated any performance
> benefits). 

This gets called from sched_switch. I expected the improvement when
we switch from monitored process to non-monitored process. With such
scenario, I tried to measure the difference in execution time of
set_dawr but I don't see any improvement. So I'll drop the patch.