From 88c7bcad71c83f52f24108dedcecae0d18dbc627 Mon Sep 17 00:00:00 2001 From: Ravi Bangoria Date: Wed, 15 Jan 2025 05:44:31 +0000 Subject: [PATCH] perf/amd/ibs: Remove pointless sample period check Valid perf event sample period value for IBS PMUs (Fetch and Op both) is limited to multiple of 0x10. perf_ibs_init() has this check: if (!event->attr.sample_freq && hwc->sample_period & 0x0f) return -EINVAL; But it's broken since hwc->sample_period will always be 0 when event->attr.sample_freq is 0 (irrespective of event->attr.freq value.) One option to fix this is to change the condition: - if (!event->attr.sample_freq && hwc->sample_period & 0x0f) + if (!event->attr.freq && hwc->sample_period & 0x0f) However, that will break all userspace tools which have been using IBS event with sample_period not multiple of 0x10. Another option is to remove the condition altogether and mask lower nibble _silently_, same as what current code is inadvertently doing. I'm preferring this approach as it keeps the existing behavior. Signed-off-by: Ravi Bangoria Signed-off-by: Peter Zijlstra (Intel) Acked-by: Namhyung Kim Link: https://lkml.kernel.org/r/20250115054438.1021-3-ravi.bangoria@amd.com --- arch/x86/events/amd/ibs.c | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c index 4ca8006d22210..bd8919e7c3b17 100644 --- a/arch/x86/events/amd/ibs.c +++ b/arch/x86/events/amd/ibs.c @@ -307,13 +307,8 @@ static int perf_ibs_init(struct perf_event *event) if (config & perf_ibs->cnt_mask) /* raw max_cnt may not be set */ return -EINVAL; - if (!event->attr.sample_freq && hwc->sample_period & 0x0f) - /* - * lower 4 bits can not be set in ibs max cnt, - * but allowing it in case we adjust the - * sample period to set a frequency. - */ - return -EINVAL; + + /* Silently mask off lower nibble. IBS hw mandates it. */ hwc->sample_period &= ~0x0FULL; if (!hwc->sample_period) hwc->sample_period = 0x10; -- 2.47.2