linux-kernel - Re: perf script: rwtop: SIGALRM and pipe read race

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Message-ID: <20120917160211.GC31375@ghostprotocols.net>
Date:	Mon, 17 Sep 2012 09:02:11 -0700
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	David Ahern <dsahern@...il.com>
Cc:	Andrew Jones <drjones@...hat.com>, linux-kernel@...r.kernel.org,
	a.p.zijlstra@...llo.nl, paulus@...ba.org, mingo@...hat.com,
	tzanussi@...il.com
Subject: Re: perf script: rwtop: SIGALRM and pipe read race

Em Mon, Sep 17, 2012 at 09:16:19AM -0600, David Ahern escreveu:
> On 9/17/12 8:55 AM, David Ahern wrote:
> >2. the rwtop.pl script is not handling negative return values ($ret < 0)
> >properly -- the '$ret > 0' check is succeeding even though $ret is
> >negative (e.g., -EAGAIN) leading to astronomical read values
> 
> I think perl is treating $ret as an unsigned integer.
> 
> Again, I know little about perl, but this change to
> ./scripts/perl/rwtop.pl makes it behave properly:
> 
>     my $n = sprintf("%d", $ret);
> 
>     if ($n > 0) {
>     ...

I think what you figured out makes sense, its the best we have and you
found it to get it back working, could you please send the two patches
properly signed-off, etc?

If Andrew could please test the patchset so that I could add his
Tested-by, that would be great,

Thanks,

- Arnaldo
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