[PATCH v2 1/5] perf: arm_spe: Add format option for discard mode
James Clark
james.clark at linaro.org
Wed Jan 8 02:08:16 PST 2025
On 07/01/2025 5:39 pm, Will Deacon wrote:
> On Tue, Dec 24, 2024 at 10:44:08AM +0000, James Clark wrote:
>> FEAT_SPEv1p2 (optional from Armv8.6) adds a discard mode that allows all
>> SPE data to be discarded rather than written to memory. Add a format
>> bit for this mode.
>>
>> If the mode isn't supported, the format bit isn't published and attempts
>> to use it will result in -EOPNOTSUPP. Allocating an aux buffer is still
>> allowed even though it won't be written to so that old tools continue to
>> work, but updated tools can choose to skip this step.
>>
>> Reviewed-by: Yeoreum Yun <yeoreum.yun at arm.com>
>> Signed-off-by: James Clark <james.clark at linaro.org>
>> ---
>> drivers/perf/arm_spe_pmu.c | 23 +++++++++++++++++++++++
>> 1 file changed, 23 insertions(+)
>>
>> diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
>> index fd5b78732603..9aaf3f98e6f5 100644
>> --- a/drivers/perf/arm_spe_pmu.c
>> +++ b/drivers/perf/arm_spe_pmu.c
>> @@ -193,6 +193,9 @@ static const struct attribute_group arm_spe_pmu_cap_group = {
>> #define ATTR_CFG_FLD_store_filter_CFG config /* PMSFCR_EL1.ST */
>> #define ATTR_CFG_FLD_store_filter_LO 34
>> #define ATTR_CFG_FLD_store_filter_HI 34
>> +#define ATTR_CFG_FLD_discard_CFG config /* PMBLIMITR_EL1.FM = DISCARD */
>> +#define ATTR_CFG_FLD_discard_LO 35
>> +#define ATTR_CFG_FLD_discard_HI 35
>>
>> #define ATTR_CFG_FLD_event_filter_CFG config1 /* PMSEVFR_EL1 */
>> #define ATTR_CFG_FLD_event_filter_LO 0
>> @@ -216,6 +219,7 @@ GEN_PMU_FORMAT_ATTR(store_filter);
>> GEN_PMU_FORMAT_ATTR(event_filter);
>> GEN_PMU_FORMAT_ATTR(inv_event_filter);
>> GEN_PMU_FORMAT_ATTR(min_latency);
>> +GEN_PMU_FORMAT_ATTR(discard);
>>
>> static struct attribute *arm_spe_pmu_formats_attr[] = {
>> &format_attr_ts_enable.attr,
>> @@ -228,9 +232,15 @@ static struct attribute *arm_spe_pmu_formats_attr[] = {
>> &format_attr_event_filter.attr,
>> &format_attr_inv_event_filter.attr,
>> &format_attr_min_latency.attr,
>> + &format_attr_discard.attr,
>> NULL,
>> };
>>
>> +static bool discard_unsupported(struct arm_spe_pmu *spe_pmu)
>> +{
>> + return spe_pmu->pmsver < ID_AA64DFR0_EL1_PMSVer_V1P2;
>> +}
>
> Why not add a new SPE_PMU_FEAT_* for this and handle it in a similar
> way to other optional hardware features?
>
> Will
Hmmm good point, I'm not sure why I didn't do it that way. Possibly
because it's only based off pmsver which is already saved, whereas the
other feats are based off reading PMSIDR which is thrown away. But I can
add SPE_PMU_FEAT_DISCARD.
Thanks
James
More information about the linux-arm-kernel
mailing list