From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To: Peter Huewe <peterhuewe@gmx.de>
Cc: Nayna Jain <nayna@linux.vnet.ibm.com>,
tpmdd-devel@lists.sourceforge.net, tpmdd@selhorst.net,
jgunthorpe@obsidianresearch.com,
linux-security-module@vger.kernel.org,
linux-kernel@vger.kernel.org,
linux-ima-devel@lists.sourceforge.net, patrickc@us.ibm.com
Subject: Re: [PATCH] tpm: improve tpm_tis send() performance by ignoring burstcount
Date: Tue, 8 Aug 2017 22:11:45 +0300 [thread overview]
Message-ID: <20170808191145.kggmoczd5laiccrn@linux.intel.com> (raw)
In-Reply-To: <E37DFCB0-2E74-45F6-B2DF-70EF59F310BC@gmx.de>
On Mon, Aug 07, 2017 at 01:52:34PM +0200, Peter Huewe wrote:
>
>
> Am 7. August 2017 13:46:32 MESZ schrieb Nayna Jain <nayna@linux.vnet.ibm.com>:
> >The TPM burstcount status indicates the number of bytes that can
> >be sent to the TPM without causing bus wait states. Effectively,
> >it is the number of empty bytes in the command FIFO. Further,
> >some TPMs have a static burstcount, when the value remains zero
> >until the entire FIFO is empty.
> >
> >This patch ignores burstcount, permitting wait states, and thus
> >writes the command as fast as the TPM can accept the bytes.
> >The performance of a 34 byte extend on a TPM 1.2 improved from
> >52 msec to 11 msec.
> >
> >Suggested-by: Ken Goldman <kgold@linux.vnet.ibm.com> in
> >conjunction with the TPM Device Driver work group.
> >Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com>
> >Acked-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
>
> Are you sure this is a good idea?
> On lpc systems this more or less stalls the bus, including keyboard/mouse (if connected via superio lpc).
>
> On which systems have you tested this?
> Spi/Lpc? Architecture?
>
> This might not be noticable for small transfers, but think about much larger transfers....
>
> Imho: NACK from my side.
>
> Thanks,
> Peter
Thanks Peter, a great insight. TPM could share the bus with other
devices. Even if this optimizes the performace for TPM it might cause
performance issues elsewhere.
One more viewpoint: TCG must added the burst count for a reason (might
be very well related what Peter said). Is ignoring it something that TCG
recommends? Not following standard exactly in the driver code sometimes
makes sense on *small details* but I would not say that this a small
detail...
After these viewpoints definitive NACK from my side too...
/Jarkko
/Jarkko
next prev parent reply other threads:[~2017-08-08 19:11 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-07 11:46 [PATCH] tpm: improve tpm_tis send() performance by ignoring burstcount Nayna Jain
2017-08-07 11:52 ` Peter Huewe
2017-08-07 14:25 ` Nayna
2017-08-08 21:50 ` Jarkko Sakkinen
2017-08-08 19:11 ` Jarkko Sakkinen [this message]
2017-08-09 20:23 ` [tpmdd-devel] " Ken Goldman
2017-08-09 20:43 ` Aw: " Peter Huewe
2017-08-11 21:54 ` Ken Goldman
[not found] ` <20170814101046.5hqrkaqmfvl7ugwj@linux.intel.com>
2017-08-16 19:51 ` Ken Goldman
2017-08-09 20:25 ` Ken Goldman
2017-08-09 21:00 ` Aw: " Peter Huewe
2017-08-11 11:14 ` Jarkko Sakkinen
2017-08-11 15:30 ` Mimi Zohar
2017-08-14 10:51 ` Jarkko Sakkinen
2017-08-14 10:56 ` Jarkko Sakkinen
2017-08-14 12:03 ` Mimi Zohar
2017-08-15 6:08 ` Jarkko Sakkinen
2017-08-14 12:12 ` Mimi Zohar
2017-08-15 6:09 ` Jarkko Sakkinen
2017-08-11 21:32 ` Aw: " Ken Goldman
2017-08-13 23:53 ` msuchanek
2017-08-15 22:02 ` Ken Goldman
2017-08-16 10:24 ` Michal Suchánek
2017-08-11 21:42 ` [Linux-ima-devel] " Ken Goldman
2017-08-08 19:07 ` Jarkko Sakkinen
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