From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga01.intel.com ([192.55.52.88]:3592 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750814AbeDXQa6 (ORCPT ); Tue, 24 Apr 2018 12:30:58 -0400 Date: Tue, 24 Apr 2018 19:30:52 +0300 From: Jarkko Sakkinen To: Nayna Jain Cc: linux-integrity@vger.kernel.org, zohar@linux.vnet.ibm.com, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, peterhuewe@gmx.de, tpmdd@selhorst.net, jgunthorpe@obsidianresearch.com, patrickc@us.ibm.com Subject: Re: [PATCH v2 2/2] tpm: reduce polling time to usecs for even finer granularity Message-ID: <20180424163052.GD5119@linux.intel.com> References: <20180417131246.434-1-nayna@linux.vnet.ibm.com> <20180417131246.434-3-nayna@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: <20180417131246.434-3-nayna@linux.vnet.ibm.com> Sender: linux-integrity-owner@vger.kernel.org List-ID: On Tue, Apr 17, 2018 at 09:12:46AM -0400, Nayna Jain wrote: > The TPM burstcount and status commands are supposed to return very > quickly [1][2]. 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 TPM 1.2 with an 8 byte burstcount for > 1000 extends improved from ~10.7 sec to ~7 sec. > > [1] From 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 us. Therefore, > even if the TPM_STS_x.burstCount field is a high value, software SHOULD > be interruptible during this period." > > [2] From 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 Great, thanks for finding those references. Kind of stuff that I will forget within months and have to revisit with git blame/log :-) Reviewed-by: Jarkko Sakkinen /Jarkko