Messages in this thread | | | Subject | Re: [PATCH v3 2/2] tpm: reduce polling time to usecs for even finer granularity | From | J Freyensee <> | Date | Tue, 8 May 2018 09:34:05 -0700 |
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On 5/7/18 9:07 AM, Nayna Jain wrote: > The TPM burstcount and status commands are supposed to return very > quickly [2][3]. This patch further reduces the TPM poll sleep time to usecs > in get_burstcount() and wait_for_tpm_stat() by calling usleep_range() > directly. > > After this change, performance on a system[1] with a TPM 1.2 with an 8 byte > burstcount for 1000 extends improved from ~10.7 sec to ~7 sec. > > [1] All tests are performed on an x86 based, locked down, single purpose > closed system. It has Infineon TPM 1.2 using LPC Bus. > > [2] From the TCG Specification "TCG PC Client Specific TPM Interface > Specification (TIS), Family 1.2": > > "NOTE : It takes roughly 330 ns per byte transfer on LPC. 256 bytes would > take 84 us, which is a long time to stall the CPU. Chipsets may not be > designed to post this much data to LPC; therefore, the CPU itself is > stalled for much of this time. Sending 1 kB would take 350 μs. Therefore, > even if the TPM_STS_x.burstCount field is a high value, software SHOULD > be interruptible during this period." > > [3] From the TCG Specification 2.0, "TCG PC Client Platform TPM Profile > (PTP) Specification": > > "It takes roughly 330 ns per byte transfer on LPC. 256 bytes would take > 84 us. Chipsets may not be designed to post this much data to LPC; > therefore, the CPU itself is stalled for much of this time. Sending 1 kB > would take 350 us. Therefore, even if the TPM_STS_x.burstCount field is a > high value, software should be interruptible during this period. For SPI, > assuming 20MHz clock and 64-byte transfers, it would take about 120 usec > to move 256B of data. Sending 1kB would take about 500 usec. If the > transactions are done using 4 bytes at a time, then it would take about > 1 msec. to transfer 1kB of data." > > Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com> > Reviewed-by: Mimi Zohar <zohar@linux.vnet.ibm.com> > Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> > ---
Acked-by: Jay Freyensee <why2jjj.linux@gmail.com>
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