From: Segher Boessenkool <segher@kernel.crashing.org>
To: Scott Wood <scottwood@freescale.com>
Cc: netdev@vger.kernel.org, jgarzik@pobox.com, linuxppc-dev@ozlabs.org
Subject: Re: [PATCH] gianfar: Add I/O barriers when touching buffer descriptor ownership.
Date: Wed, 2 May 2007 20:05:43 +0200 [thread overview]
Message-ID: <4334c860f893dbc537a51999cea25532@kernel.crashing.org> (raw)
In-Reply-To: <4638B673.4090504@freescale.com>
>> AFAICS you need stronger barriers though; {w,r,}mb(),
>> to prevent _any_ reordering of those memory accesses,
>> not just the compiler-generated ones.
>
> My impression was that the eieio used by iobarrier would be sufficient
> for that, as we're not trying to synchronize between accesses to
> different types of memory. Is sync really required here?
For accesses to main system memory, eieio only orders
writes, not reads, so iobarrier_r() doesn't do what
you want; and iobarrier_w() isn't meant to be used for
main memory access ordering either.
Also, it is better to not use powerpc-specific interfaces
in a device driver if you don't have a strong reason to.
Segher
WARNING: multiple messages have this Message-ID (diff)
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Scott Wood <scottwood@freescale.com>
Cc: netdev@vger.kernel.org, linuxppc-dev@ozlabs.org, jgarzik@pobox.com
Subject: Re: [PATCH] gianfar: Add I/O barriers when touching buffer descriptor ownership.
Date: Wed, 2 May 2007 20:05:43 +0200 [thread overview]
Message-ID: <4334c860f893dbc537a51999cea25532@kernel.crashing.org> (raw)
In-Reply-To: <4638B673.4090504@freescale.com>
>> AFAICS you need stronger barriers though; {w,r,}mb(),
>> to prevent _any_ reordering of those memory accesses,
>> not just the compiler-generated ones.
>
> My impression was that the eieio used by iobarrier would be sufficient
> for that, as we're not trying to synchronize between accesses to
> different types of memory. Is sync really required here?
For accesses to main system memory, eieio only orders
writes, not reads, so iobarrier_r() doesn't do what
you want; and iobarrier_w() isn't meant to be used for
main memory access ordering either.
Also, it is better to not use powerpc-specific interfaces
in a device driver if you don't have a strong reason to.
Segher
next prev parent reply other threads:[~2007-05-02 18:05 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-01 16:55 [PATCH] gianfar: Add I/O barriers when touching buffer descriptor ownership Scott Wood
2007-05-02 0:54 ` Segher Boessenkool
2007-05-02 0:54 ` Segher Boessenkool
2007-05-02 16:04 ` Scott Wood
2007-05-02 16:04 ` Scott Wood
2007-05-02 18:05 ` Segher Boessenkool [this message]
2007-05-02 18:05 ` Segher Boessenkool
-- strict thread matches above, loose matches on Subject: below --
2007-05-16 20:06 Scott Wood
2007-05-18 0:45 ` Jeff Garzik
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