From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Stancek Date: Fri, 11 Aug 2017 07:26:06 -0400 (EDT) Subject: [LTP] [PATCH 2/2] syscalls/pselect: Add a zero latency constraint In-Reply-To: References: <1502352088-10136-1-git-send-email-daniel.lezcano@linaro.org> <1502352088-10136-2-git-send-email-daniel.lezcano@linaro.org> <1cbcc5dd-e060-94df-982e-198b3b342ec6@redhat.com> Message-ID: <1217268944.70548669.1502450766723.JavaMail.zimbra@redhat.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: ltp@lists.linux.it ----- Original Message ----- > On 10/08/2017 13:50, Jiri Jaburek wrote: > > On 08/10/17 10:01, Daniel Lezcano wrote: > >> The pselect_01 testcase works well on an x86 as it is a fast platform, > >> with > >> fast exit latency idle routine. > >> > >> However on ARM[64] the idle routine can take much more time, for example > >> 1500us. > >> > >> The pselect fails on the ARM[64] platforms because of these slow exit > >> latencies, > >> the delay between the expected expiration and the observed one is not > >> acceptable. > >> > >> The fix could be to increase the deviation on ARM64 but that wouldn't make > >> sense as some platforms, for the same architecture, can have faster or > >> different delays, hence we can potentially miss a bug. > >> > >> The simplest solution is to set the cpu_dma latency constraint to zero, so > >> the > >> idle driver will always choose the fastest idle state, thus fixing the > >> issue > >> above. The latency constraint will apply only for this test. > > > > I think a more generic LTP-wide solution could be made; there are more > > tests that fail ie. on virtualized environments because of CPU over- > > provisioning on the host (x86, s390, ppc, etc.) > > Not sure a latency constraint will fix the above. We could detect bare-metal / (some [1]) virt and adjust threshold for timer tests, but I'm assuming Daniel sees this on bare metal, so this patch would be useful anyway. [1] kvm/xen is easy to detect, lpars might be more tricky Regards, Jan