netdev - Re: [PATCH/RFC] net: Add __napi_sycnhronize() to sync with napi poll

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Message-ID: <47157EA4.1000500@garzik.org>
Date:	Tue, 16 Oct 2007 23:16:52 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	benh@...nel.crashing.org
CC:	Stephen Hemminger <shemminger@...ux-foundation.org>,
	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Roland Dreier <rdreier@...co.com>,
	linuxppc-dev list <linuxppc-dev@...abs.org>
Subject: Re: [PATCH/RFC] net: Add __napi_sycnhronize() to sync with napi	poll

Benjamin Herrenschmidt wrote:
> net: Add __napi_synchronize() to sync with napi poll
> 
> The EMAC driver which needs to handle multiple devices with one
> NAPI instance implements its own per-channel disable bit. However,
> when setting such a bit, it needs to synchronize with the poller
> (that is make sure that any pending poller instance has completed,
> or is started late enough to see that disable bit).
> 
> This implements a low level __napi_synchronize() function to acheive
> that. The underscores are to emphasis the low level aspect of it and
> to discourage driver writers who don't know what they are doing to
> use it (to please DaveM :-)
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> ---
> 
> Switched to do a cpu_relax() spin instead and only on SMP. Not that
> we have an smp_mb() in there which synchronize_irq() lacks. I believe
> this is a bug in synchronize_irq() which I'll handle separately.
> 
> Note: unfortunately, Jeff already picked up the EMAC patch without
> waiting for this to be sorted out (oops...). So if you agree with
> this patch, it would be nice to have it go in quickly or maybe via
> Jeff's tree to avoid breakage ? Not terribly important tho.


Sorry, I thought that was the way everybody was headed.  With the driver 
broken /anyway/, I just sorta threw it into the pile of fixes.

It's upstream now, so let me know if you want to revert or move forward 
from here...

	Jeff


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