Re: [PATCH v2 1/9] perf: Add EVENT_ATTR_ID to simplify event attributes
From: liuqi (BA)
Date: Wed Jun 02 2021 - 06:51:35 EST
Hi Will,
On 2021/6/2 17:49, Will Deacon wrote:
On Wed, Jun 02, 2021 at 04:45:23PM +0800, liuqi (BA) wrote:
Hi Will,
Thanks for reviewing this patch.
On 2021/6/1 21:10, Will Deacon wrote:
On Wed, May 19, 2021 at 05:51:51PM +0800, Qi Liu wrote:
Similar EVENT_ATTR macros are defined in many PMU drivers,
like HiSilicon PMU driver, Arm PMU driver, Arm SMMU PMU
driver. So Add a generic macro to simplify code.
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Signed-off-by: Qi Liu <liuqi115@xxxxxxxxxx>
---
include/linux/perf_event.h | 6 ++++++
kernel/events/core.c | 2 ++
2 files changed, 8 insertions(+)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index f5a6a2f..d0aa74e 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1576,6 +1576,12 @@ static struct perf_pmu_events_attr _var = { \
.event_str = _str, \
};
+#define PMU_EVENT_ATTR_ID(_name, _id) \
+ (&((struct perf_pmu_events_attr[]) { \
+ { .attr = __ATTR(_name, 0444, perf_event_sysfs_show, NULL), \
+ .id = _id, } \
+ })[0].attr.attr)
+
#define PMU_FORMAT_ATTR(_name, _format) \
static ssize_t \
_name##_show(struct device *dev, \
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0ac818b..330d9cc 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -13295,6 +13295,8 @@ ssize_t perf_event_sysfs_show(struct device *dev, struct device_attribute *attr,
if (pmu_attr->event_str)
return sprintf(page, "%s\n", pmu_attr->event_str);
+ else
+ return sprintf(page, "config=%#llx\n", pmu_attr->id);
I think it's a really bad idea to hardcode this here. For example, I think
this patch series breaks user ABI for the SMMU PMU which used to print:
"event=0x%02llx\n"
and by the looks of it many of the other conversions are unsound too.
Got it, so I'll use pmu_attr->event_str here, for example,
SMMU_EVENT_ATTR(cycles, "event=0x00")
You could, but honestly I don't really see this being any better than the
current code. The advantage of using "event=0x%02llx\n" is that things are
consistent by construction and therefore userspace can parse the information
easily. We lose that if we just hardcode the string and it's error-prone to
extend.
Will
Got it, thanks.
So how about adding a common macro like this:
#define PMU_EVENT_ATTR_ID(_name,_func, _id) \
(&((struct perf_pmu_events_attr[]) { \
{ .attr = __ATTR(_name, 0444, _func, NULL), \
.id = _id, } \
})[0].attr.attr)
Drivers could define thir private macro, like SMMU_PMU_EVENT_ATTR, and
use their private event_show() functions if they need, or use the common
function perf_event_sysfs_show().
Thanks,
Qi
.