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From: David Miller <davem@davemloft.net>
To: scottwood@freescale.com
Cc: David.Laight@ACULAB.COM, netdev@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v2] gianfar: Fall back to software tcp/udp checksum on oldercontrollers
Date: Fri, 28 Jan 2011 11:59:39 -0800 (PST)	[thread overview]
Message-ID: <20110128.115939.104064843.davem@davemloft.net> (raw)
In-Reply-To: <20110128105610.4a518456@udp111988uds.am.freescale.net>

From: Scott Wood <scottwood@freescale.com>
Date: Fri, 28 Jan 2011 10:56:10 -0600

> On Fri, 28 Jan 2011 09:10:46 +0000
> David Laight <David.Laight@ACULAB.COM> wrote:
> 
>>  
>> > +		if (unlikely(gfar_has_errata(priv, GFAR_ERRATA_12)
>> > +			     && ((unsigned long)fcb % 0x20) > 0x18)) {
>> 
>> You need to check the generated code, but I think you need:
>> 
>>     if (unlikely(gfar_has_errata(priv, GFAR_ERRATA_12))
>> 	     && unlikely(((unsigned long)fcb % 0x20) > 0x18))
>> 
>> ie unlikely() around both the primitive comparisons.
> 
> Is the first condition actually unlikely?  If you've got affected
> hardware, you'll hit it every time.
> 
> If packets with the problematic alignment are rare, seems like it'd be
> better to check that first.

In cases like this gfar_has_errata() case, better to leave it's
likelyhood unmarked.

And yes, since it's cheaper, checking the alignment should be done
first.

WARNING: multiple messages have this Message-ID (diff)
From: David Miller <davem@davemloft.net>
To: scottwood@freescale.com
Cc: netdev@vger.kernel.org, David.Laight@ACULAB.COM,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v2] gianfar: Fall back to software tcp/udp checksum on oldercontrollers
Date: Fri, 28 Jan 2011 11:59:39 -0800 (PST)	[thread overview]
Message-ID: <20110128.115939.104064843.davem@davemloft.net> (raw)
In-Reply-To: <20110128105610.4a518456@udp111988uds.am.freescale.net>

From: Scott Wood <scottwood@freescale.com>
Date: Fri, 28 Jan 2011 10:56:10 -0600

> On Fri, 28 Jan 2011 09:10:46 +0000
> David Laight <David.Laight@ACULAB.COM> wrote:
> 
>>  
>> > +		if (unlikely(gfar_has_errata(priv, GFAR_ERRATA_12)
>> > +			     && ((unsigned long)fcb % 0x20) > 0x18)) {
>> 
>> You need to check the generated code, but I think you need:
>> 
>>     if (unlikely(gfar_has_errata(priv, GFAR_ERRATA_12))
>> 	     && unlikely(((unsigned long)fcb % 0x20) > 0x18))
>> 
>> ie unlikely() around both the primitive comparisons.
> 
> Is the first condition actually unlikely?  If you've got affected
> hardware, you'll hit it every time.
> 
> If packets with the problematic alignment are rare, seems like it'd be
> better to check that first.

In cases like this gfar_has_errata() case, better to leave it's
likelyhood unmarked.

And yes, since it's cheaper, checking the alignment should be done
first.

  reply	other threads:[~2011-01-28 19:59 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-27  8:14 [PATCH] gianfar: Fall back to software tcp/udp checksum on older controllers Alex Dubov
2011-01-27  9:51 ` Anton Vorontsov
2011-01-27 22:23   ` David Miller
2011-01-28  2:43   ` Alex Dubov
2011-01-28  4:37   ` [PATCH v2] " Alex Dubov
2011-01-28  4:37     ` Alex Dubov
2011-01-28  9:10     ` [PATCH v2] gianfar: Fall back to software tcp/udp checksum on oldercontrollers David Laight
2011-01-28  9:10       ` David Laight
2011-01-28 16:56       ` Scott Wood
2011-01-28 16:56         ` Scott Wood
2011-01-28 19:59         ` David Miller [this message]
2011-01-28 19:59           ` David Miller

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