From: David Laight <David.Laight@ACULAB.COM>
To: 'Eric Dumazet' <eric.dumazet@gmail.com>,
Alexander Duyck <alexander.duyck@gmail.com>
Cc: David Miller <davem@davemloft.net>,
netdev <netdev@vger.kernel.org>,
"Tariq Toukan" <tariqt@mellanox.com>,
Saeed Mahameed <saeedm@mellanox.com>
Subject: RE: [PATCH v2 net] net: solve a NAPI race
Date: Thu, 2 Mar 2017 10:24:42 +0000 [thread overview]
Message-ID: <063D6719AE5E284EB5DD2968C1650D6DCFE733A0@AcuExch.aculab.com> (raw)
In-Reply-To: <1488389559.9415.300.camel@edumazet-glaptop3.roam.corp.google.com>
From: Eric Dumazet
> Sent: 01 March 2017 17:33
> On Wed, 2017-03-01 at 08:14 -0800, Alexander Duyck wrote:
>
> > What build flags are you using? With -Os or -O2 I have seen it
> > convert the /b * c into a single shift.
> >
>
>
> Because b & c are unsigned in our case.
>
> I presume David tried signed integers, this is why gcc does that.
I was using integer constants but an unsigned variable.
Changing the constants to unsigned makes no difference (they would get
promoted anyway).
After some experiments I can get gcc to generate a single shift if the
variable being tested is 32bits, the constants are 64bits and a 64bit
result is required.
In every other case it does either and-shr-shl or shr-and-shl (all the
shr are logical).
David
prev parent reply other threads:[~2017-03-02 10:25 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-25 14:22 [PATCH net] net/mlx4_en: reception NAPI/IRQ race breaker Eric Dumazet
2017-02-26 16:32 ` Saeed Mahameed
2017-02-26 17:34 ` Eric Dumazet
2017-02-26 17:40 ` Eric Dumazet
2017-02-26 18:03 ` Eric Dumazet
2017-02-27 3:31 ` [PATCH net] net: solve a NAPI race Eric Dumazet
2017-02-27 14:06 ` Eric Dumazet
2017-02-27 14:21 ` [PATCH v2 " Eric Dumazet
2017-02-27 16:19 ` David Miller
2017-02-27 16:44 ` Eric Dumazet
2017-02-27 17:10 ` Eric Dumazet
2017-02-28 2:08 ` David Miller
2017-03-01 0:22 ` Francois Romieu
2017-03-01 1:04 ` Stephen Hemminger
2017-02-27 21:00 ` Alexander Duyck
2017-02-27 20:18 ` [PATCH v3 " Eric Dumazet
2017-02-27 22:14 ` Stephen Hemminger
2017-02-27 22:35 ` Eric Dumazet
2017-02-27 22:44 ` Stephen Hemminger
2017-02-27 22:48 ` David Miller
2017-02-27 23:23 ` Stephen Hemminger
2017-02-28 10:14 ` David Laight
2017-02-28 13:04 ` Eric Dumazet
2017-02-28 13:20 ` Eric Dumazet
2017-02-28 16:17 ` Stephen Hemminger
2017-02-28 16:57 ` Eric Dumazet
2017-02-28 18:34 ` [PATCH v4 " Eric Dumazet
2017-03-01 17:53 ` David Miller
2017-02-28 17:20 ` [PATCH v2 " Alexander Duyck
2017-02-28 17:47 ` Eric Dumazet
2017-03-01 10:41 ` David Laight
2017-03-01 16:14 ` Alexander Duyck
2017-03-01 17:32 ` Eric Dumazet
2017-03-02 10:24 ` David Laight [this message]
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