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Message-ID: <523ADD8D.1030607@intel.com>
Date: Thu, 19 Sep 2013 14:18:37 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: Ingo Molnar <mingo@...nel.org>
CC: Peter Zijlstra <peterz@...radead.org>,
Vince Weaver <vince@...ter.net>, hpa@...or.com,
linux-kernel@...r.kernel.org, tglx@...utronix.de,
linux-tip-commits@...r.kernel.org, eranian@...glemail.com
Subject: Re: [PATCH, v3] perf: Always set bit 0 in the capabilities field
of 'struct perf_event_mmap_page' to 0, to maintain the ABI
On 19/09/13 13:40, Ingo Molnar wrote:
>
> * Peter Zijlstra <peterz@...radead.org> wrote:
>
>> On Thu, Sep 19, 2013 at 12:28:18PM +0200, Ingo Molnar wrote:
>>
>> You really don't like version fields do you ;-)
>
> Indeed they are a horrible concept.
>
>> Would it make sense to do something like s/cap_usr/cap_user/ and drop
>> the _available, _used postfixes? It results in different names but
>> avoids these terribly long ones.
>
> Absolutely! Find updated patch below.
>
> Thanks,
>
> Ingo
>
> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
> index 8355c84..a9c606b 100644
> --- a/arch/x86/kernel/cpu/perf_event.c
> +++ b/arch/x86/kernel/cpu/perf_event.c
> @@ -1883,9 +1883,9 @@ static struct pmu pmu = {
>
> void arch_perf_update_userpage(struct perf_event_mmap_page *userpg, u64 now)
> {
> - userpg->cap_usr_time = 0;
> - userpg->cap_usr_time_zero = 0;
> - userpg->cap_usr_rdpmc = x86_pmu.attr_rdpmc;
> + userpg->cap_user_time = 0;
> + userpg->cap_user_time_zero = 0;
> + userpg->cap_user_rdpmc = x86_pmu.attr_rdpmc;
> userpg->pmc_width = x86_pmu.cntval_bits;
>
> if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
> @@ -1894,13 +1894,13 @@ void arch_perf_update_userpage(struct perf_event_mmap_page *userpg, u64 now)
> if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC))
> return;
>
> - userpg->cap_usr_time = 1;
> + userpg->cap_user_time = 1;
> userpg->time_mult = this_cpu_read(cyc2ns);
> userpg->time_shift = CYC2NS_SCALE_FACTOR;
> userpg->time_offset = this_cpu_read(cyc2ns_offset) - now;
>
> if (sched_clock_stable && !check_tsc_disabled()) {
> - userpg->cap_usr_time_zero = 1;
> + userpg->cap_user_time_zero = 1;
> userpg->time_zero = this_cpu_read(cyc2ns_offset);
> }
> }
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 40a1fb8..dd4c903 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -380,10 +380,13 @@ struct perf_event_mmap_page {
> union {
> __u64 capabilities;
> struct {
> - __u64 cap_usr_time : 1,
> - cap_usr_rdpmc : 1,
> - cap_usr_time_zero : 1,
> - cap_____res : 61;
> + __u64 cap_bit0 : 1, /* Always 0, deprecated, see commit 860f085b74e9 */
> + cap_bit0_is_deprecated : 1, /* Always 1, signals that bit 0 is zero */
> +
> + cap_user_rdpmc : 1, /* The RDPMC instruction can be used to read counts */
> + cap_user_time : 1, /* The time_* fields are used */
> + cap_user_time_zero : 1, /* The time_zero field is used */
> + cap_____res : 59;
> };
> };
>
> @@ -442,12 +445,13 @@ struct perf_event_mmap_page {
> * ((rem * time_mult) >> time_shift);
> */
> __u64 time_zero;
> + __u32 size; /* Header size up to __reserved[] fields. */
>
> /*
> * Hole for extension of the self monitor capabilities
> */
>
> - __u64 __reserved[119]; /* align to 1k */
> + __u8 __reserved[118*8+4]; /* align to 1k. */
>
> /*
> * Control data for the mmap() data buffer.
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index dd236b6..cb4238e 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -3660,6 +3660,26 @@ static void calc_timer_values(struct perf_event *event,
> *running = ctx_time - event->tstamp_running;
> }
>
> +static void perf_event_init_userpage(struct perf_event *event)
> +{
> + struct perf_event_mmap_page *userpg;
> + struct ring_buffer *rb;
> +
> + rcu_read_lock();
> + rb = rcu_dereference(event->rb);
> + if (!rb)
> + goto unlock;
> +
> + userpg = rb->user_page;
> +
> + /* Allow new userspace to detect that bit 0 is deprecated */
> + userpg->cap_bit0_is_deprecated = 1;
> + userpg->size = offsetof(struct perf_event_mmap_page, __reserved);
> +
> +unlock:
> + rcu_read_unlock();
> +}
> +
> void __weak arch_perf_update_userpage(struct perf_event_mmap_page *userpg, u64 now)
> {
> }
> @@ -4044,6 +4064,7 @@ again:
> ring_buffer_attach(event, rb);
> rcu_assign_pointer(event->rb, rb);
>
> + perf_event_init_userpage(event);
> perf_event_update_userpage(event);
>
> unlock:
>
>
Please consider adding:
diff --git a/tools/perf/arch/x86/util/tsc.c b/tools/perf/arch/x86/util/tsc.c
index 9570c2b..b2519e4 100644
--- a/tools/perf/arch/x86/util/tsc.c
+++ b/tools/perf/arch/x86/util/tsc.c
@@ -32,7 +32,7 @@ u64 tsc_to_perf_time(u64 cyc, struct perf_tsc_conversion *tc)
int perf_read_tsc_conversion(const struct perf_event_mmap_page *pc,
struct perf_tsc_conversion *tc)
{
- bool cap_usr_time_zero;
+ bool cap_user_time_zero;
u32 seq;
int i = 0;
@@ -42,7 +42,7 @@ int perf_read_tsc_conversion(const struct
perf_event_mmap_page *pc,
tc->time_mult = pc->time_mult;
tc->time_shift = pc->time_shift;
tc->time_zero = pc->time_zero;
- cap_usr_time_zero = pc->cap_usr_time_zero;
+ cap_user_time_zero = pc->cap_user_time_zero;
rmb();
if (pc->lock == seq && !(seq & 1))
break;
@@ -52,7 +52,7 @@ int perf_read_tsc_conversion(const struct
perf_event_mmap_page *pc,
}
}
- if (!cap_usr_time_zero)
+ if (!cap_user_time_zero)
return -EOPNOTSUPP;
return 0;
--
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