Re: [PATCH 1/4] perf: Add 'flags' parameter to pmu txn interfaces

From: Peter Zijlstra
Date: Tue Mar 17 2015 - 02:47:58 EST


On Wed, Mar 04, 2015 at 12:35:05AM -0800, Sukadev Bhattiprolu wrote:
> In addition to using the transaction interface to schedule events
> on a PMU, we will use it to also read a group of counters at once.
> Accordingly, add a flags parameter to the transaction interfaces.
> The flags indicate wheether the transaction is to add events to
> the PMU (PERF_PMU_TXN_ADD) or to read the events PERF_PMU_TXN_READ.
>
> Based on input from Peter Zijlstra.
>
> Signed-off-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
> ---
> arch/powerpc/perf/core-book3s.c | 15 ++++++++++++---
> arch/x86/kernel/cpu/perf_event.c | 15 ++++++++++++---
> include/linux/perf_event.h | 14 +++++++++++---
> kernel/events/core.c | 26 +++++++++++++++-----------
> 4 files changed, 50 insertions(+), 20 deletions(-)

s390 and sparc also implement the txn.

# git grep "\.start_txn"
arch/powerpc/perf/core-book3s.c: .start_txn = power_pmu_start_txn,
arch/s390/kernel/perf_cpum_cf.c: .start_txn = cpumf_pmu_start_txn,
arch/sparc/kernel/perf_event.c: .start_txn = sparc_pmu_start_txn,
arch/x86/kernel/cpu/perf_event.c: .start_txn = x86_pmu_start_txn,

Also; you add the flag to all 3 calls; does it make sense to only pass
it to the first and save the txn type in the txn state itself? We could
add PERF_EVENT_TXN_READ for this..
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