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Date: Thu, 05 Sep 2013 14:25:30 -0400 (EDT)
Message-Id: <20130905.142530.732425484460470485.davem@davemloft.net>
To: Vineet.Gupta1@synopsys.com
Cc: netdev@vger.kernel.org, Alexey.Brodkin@synopsys.com,
        linux-kernel@vger.kernel.org, arc-linux-dev@synopsys.com
Subject: Re: [PATCH] ethernet/arc/arc_emac: Fix huge delays in large file
 copies
From: David Miller <davem@davemloft.net>
In-Reply-To: <1378295235-18928-1-git-send-email-vgupta@synopsys.com>
References: <1378295235-18928-1-git-send-email-vgupta@synopsys.com>
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From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Date: Wed, 4 Sep 2013 17:17:15 +0530

> copying large files to a NFS mounted host was taking absurdly large
> time.
> 
> Turns out that TX BD reclaim had a sublte bug.
> 
> Loop starts off from @txbd_dirty cursor and stops when it hits a BD
> still in use by controller. However when it stops it needs to keep the
> cursor at that very BD to resume scanning in next iteration. However it
> was erroneously incrementing the cursor, causing the next scan(s) to
> fail too, unless the BD chain was completely drained out.
> 
> [ARCLinux]$ ls -l -sh /disk/log.txt
>  17976 -rw-r--r--    1 root     root       17.5M Sep  /disk/log.txt
> 
> ========== Before =====================
> [ARCLinux]$ time cp /disk/log.txt /mnt/.
> real    31m 7.95s
> user    0m 0.00s
> sys     0m 0.10s
> 
> ========== After =====================
> [ARCLinux]$ time cp /disk/log.txt /mnt/.
> real    0m 24.33s
> user    0m 0.00s
> sys     0m 0.19s
> 
> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

Applied.