From mboxrd@z Thu Jan 1 00:00:00 1970 From: why2jjj.linux@gmail.com (J Freyensee) Date: Tue, 8 May 2018 09:34:05 -0700 Subject: [PATCH v3 2/2] tpm: reduce polling time to usecs for even finer granularity In-Reply-To: <20180507160733.8817-3-nayna@linux.vnet.ibm.com> References: <20180507160733.8817-1-nayna@linux.vnet.ibm.com> <20180507160733.8817-3-nayna@linux.vnet.ibm.com> Message-ID: To: linux-security-module@vger.kernel.org List-Id: linux-security-module.vger.kernel.org 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 ?s. 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 > Reviewed-by: Mimi Zohar > Reviewed-by: Jarkko Sakkinen > --- Acked-by: Jay Freyensee -- 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