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Re: some question about wmb in mips

To: loody <miloody@gmail.com>
Subject: Re: some question about wmb in mips
From: Ralf Baechle <ralf@linux-mips.org>
Date: Sun, 27 Jun 2010 21:39:40 +0100
Cc: Linux MIPS Mailing List <linux-mips@linux-mips.org>
In-reply-to: <AANLkTikXife5CaPBQ4k_FUUM6-VD2C7SOOEbyugRhIqG@mail.gmail.com>
References: <AANLkTikXife5CaPBQ4k_FUUM6-VD2C7SOOEbyugRhIqG@mail.gmail.com>
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On Mon, Jun 28, 2010 at 12:16:06AM +0800, loody wrote:

> Dear all:
> AFAIK, wmb in mips is implemented by calling sync,
> wmb->fast_wmb->__sync, which makes sure Loads and stores executed
> before the SYNC are completed before loads
> and stores after the SYNC can start
> But will this instruction write the cache back too?

No.

> take usb example, it will call this maco before it let host processing
> the commands on dram, so I wondering whether sync will write the cache
> back to memory.

SYNC is for memory consistency, not coherency.

  Ralf

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