From mboxrd@z Thu Jan 1 00:00:00 1970 From: jarkko.sakkinen@linux.intel.com (Jarkko Sakkinen) Date: Tue, 8 Aug 2017 22:11:45 +0300 Subject: [PATCH] tpm: improve tpm_tis send() performance by ignoring burstcount In-Reply-To: References: <20170807114632.1339-1-nayna@linux.vnet.ibm.com> Message-ID: <20170808191145.kggmoczd5laiccrn@linux.intel.com> To: linux-security-module@vger.kernel.org List-Id: linux-security-module.vger.kernel.org On Mon, Aug 07, 2017 at 01:52:34PM +0200, Peter Huewe wrote: > > > Am 7. August 2017 13:46:32 MESZ schrieb Nayna Jain : > >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 in > >conjunction with the TPM Device Driver work group. > >Signed-off-by: Nayna Jain > >Acked-by: Mimi Zohar > > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html