Messages in this thread Patch in this message | | | From | Alexander Shishkin <> | Subject | [PATCH v7 04/14] perf: Add a capability for AUX_NO_SG pmus to do software double buffering | Date | Tue, 11 Nov 2014 16:48:18 +0200 |
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For pmus that don't support scatter-gather for AUX data in hardware, it might still make sense to implement software double buffering to avoid losing data while the user is reading data out. For this purpose, add a pmu capability that guarantees multiple high-order chunks for AUX buffer, so that the pmu driver can do switchover tricks.
To make use of this feature, add PERF_PMU_CAP_AUX_SW_DOUBLEBUF to your pmu's capability mask. This will make the ring buffer AUX allocation code ensure that the biggest high order allocation for the aux buffer pages is no bigger than half of the total requested buffer size, thus making sure that the buffer has at least two high order allocations.
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com> --- include/linux/perf_event.h | 1 + kernel/events/ring_buffer.c | 15 ++++++++++++++- 2 files changed, 15 insertions(+), 1 deletion(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 71df948b4d..e7a15f5c3f 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -172,6 +172,7 @@ struct perf_event; */ #define PERF_PMU_CAP_NO_INTERRUPT 0x01 #define PERF_PMU_CAP_AUX_NO_SG 0x02 +#define PERF_PMU_CAP_AUX_SW_DOUBLEBUF 0x04 /** * struct pmu - generic performance monitoring unit diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index ae49a9bd11..1b4b593a32 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -286,9 +286,22 @@ int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event, if (!has_aux(event)) return -ENOTSUPP; - if (event->pmu->capabilities & PERF_PMU_CAP_AUX_NO_SG) + if (event->pmu->capabilities & PERF_PMU_CAP_AUX_NO_SG) { max_order = get_order(nr_pages * PAGE_SIZE); + /* + * PMU requests more than one contiguous chunks of memory + * for SW double buffering + */ + if ((event->pmu->capabilities & PERF_PMU_CAP_AUX_SW_DOUBLEBUF) && + !overwrite) { + if (!max_order) + return -EINVAL; + + max_order--; + } + } + rb->aux_pages = kzalloc_node(nr_pages * sizeof(void *), GFP_KERNEL, node); if (!rb->aux_pages) return -ENOMEM; -- 2.1.1
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