From: Robert Stonehouse <rstonehouse@solarflare•com>
To: David Miller <davem@davemloft•net>
Cc: <sshah@solarflare•com>, <netdev@vger•kernel.org>,
<linux-net-drivers@solarflare•com>
Subject: Re: [PATCH net v4 1/2] sfc: use 64-bit writes for PIO.
Date: Thu, 5 Jun 2014 18:08:48 +0100 [thread overview]
Message-ID: <5390A420.9070903@solarflare.com> (raw)
In-Reply-To: <20140603.155807.2227032324368753328.davem@davemloft.net>
On 03/06/14 23:58, David Miller wrote:
> Did you do any functional testing of this on such a machine?
>
> I'm extremely disappointed in this patch submission, because you
> didn't even_compile_ test this in the environment where you claim
> the problem exists.
The next patch posted in the series would have meant that this change
was limited to x86_64 systems.
I am sorry that by posting the patches in an incorrect order/not merging
them we gave the impression that we do not test these patches (but hands
up, patch 1/2 did break 32 bit compiles and certainly did need more
work. Thanks to Sergei, Joe and yourself for comments)
For x86_64 machines we checked writeq() implementations in io.h and
disassembled the module to ensure that a single 64bit access was used.
I would like to get an improved bug fix upstream, as I know this rare
hardware issue has been hit in the wild and with TX checksum offload
enabled corrupted data can get to the application.
The reason for limiting to x86_64 is that in this code path there is an
IO write to a write-combined mapping. It was a very hard case to hit
(believed to depend on the timing of accesses and resulting
write-combining behaviour), but we never reproduced it in our lab.
Limiting this IO to WC mappings to x86_64 only was a safety measure
given the amount of hours of testing we have on x86_64 vs.other 64 bit
platforms that we test with (PPC64)
This feature gives a small latency win on this hardware family for small
packets.
Unless there are more comments to consider the next post will be a
merged patch, addressing all points raised so far.
Regards
Rob
next prev parent reply other threads:[~2014-06-05 17:08 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-03 10:02 [PATCH net v4 0/2] sfc: Restrict PIO for 64bit arch in order to avoid data corruption Shradha Shah
2014-06-03 10:04 ` [PATCH net v4 1/2] sfc: use 64-bit writes for PIO Shradha Shah
2014-06-03 16:45 ` Sergei Shtylyov
2014-06-03 17:55 ` Joe Perches
2014-06-03 22:58 ` David Miller
2014-06-05 17:08 ` Robert Stonehouse [this message]
2014-06-03 10:05 ` [PATCH net v4 2/2] sfc: Restrict PIO to 64-bit architectures Shradha Shah
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