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Message-ID: <20241007034810.754-3-ravi.bangoria@amd.com>
Date: Mon, 7 Oct 2024 03:48:04 +0000
From: Ravi Bangoria <ravi.bangoria@....com>
To: <peterz@...radead.org>, <mingo@...hat.com>, <namhyung@...nel.org>
CC: <ravi.bangoria@....com>, <acme@...nel.org>, <eranian@...gle.com>,
<mark.rutland@....com>, <alexander.shishkin@...ux.intel.com>,
<jolsa@...nel.org>, <irogers@...gle.com>, <adrian.hunter@...el.com>,
<kan.liang@...ux.intel.com>, <tglx@...utronix.de>, <bp@...en8.de>,
<dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
<linux-perf-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<santosh.shukla@....com>, <ananth.narayan@....com>, <sandipan.das@....com>
Subject: [PATCH 2/8] 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 <ravi.bangoria@....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 347353b9eb70..6b55a8520166 100644
--- a/arch/x86/events/amd/ibs.c
+++ b/arch/x86/events/amd/ibs.c
@@ -294,13 +294,8 @@ 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;
--
2.46.2
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