From: Mathieu Desnoyers Date: Mon, 19 Sep 2016 01:38:38 +0000 (-0400) Subject: Performance: Only dereference shmp once X-Git-Tag: v2.9.0-rc1~15 X-Git-Url: http://git.liburcu.org/?p=lttng-ust.git;a=commitdiff_plain;h=d2fe4771f15b6e50969bea1d7fcd74edca307de3 Performance: Only dereference shmp once Dereferencing shared-memory pointers is expensive: many bound checks are performed. Ensure the shmp is only dereferenced once in the commit fast-path. Signed-off-by: Mathieu Desnoyers --- diff --git a/libringbuffer/frontend_api.h b/libringbuffer/frontend_api.h index 5ddb8ac4..eea2a8db 100644 --- a/libringbuffer/frontend_api.h +++ b/libringbuffer/frontend_api.h @@ -250,6 +250,8 @@ void lib_ring_buffer_commit(const struct lttng_ust_lib_ring_buffer_config *confi unsigned long offset_end = ctx->buf_offset; unsigned long endidx = subbuf_index(offset_end - 1, chan); unsigned long commit_count; + struct commit_counters_hot *cc_hot = shmp_index(handle, + buf->commit_hot, endidx); /* * Must count record before incrementing the commit count. @@ -262,7 +264,7 @@ void lib_ring_buffer_commit(const struct lttng_ust_lib_ring_buffer_config *confi */ cmm_smp_wmb(); - v_add(config, ctx->slot_size, &shmp_index(handle, buf->commit_hot, endidx)->cc); + v_add(config, ctx->slot_size, &cc_hot->cc); /* * commit count read can race with concurrent OOO commit count updates. @@ -282,7 +284,7 @@ void lib_ring_buffer_commit(const struct lttng_ust_lib_ring_buffer_config *confi * count reaches back the reserve offset for a specific sub-buffer, * which is completely independent of the order. */ - commit_count = v_read(config, &shmp_index(handle, buf->commit_hot, endidx)->cc); + commit_count = v_read(config, &cc_hot->cc); lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1, commit_count, endidx, handle, ctx->tsc); @@ -290,8 +292,8 @@ void lib_ring_buffer_commit(const struct lttng_ust_lib_ring_buffer_config *confi * Update used size at each commit. It's needed only for extracting * ring_buffer buffers from vmcore, after crash. */ - lib_ring_buffer_write_commit_counter(config, buf, chan, endidx, - offset_end, commit_count, handle); + lib_ring_buffer_write_commit_counter(config, buf, chan, + offset_end, commit_count, handle, cc_hot); } /** diff --git a/libringbuffer/frontend_internal.h b/libringbuffer/frontend_internal.h index c973e6b2..10d6c4db 100644 --- a/libringbuffer/frontend_internal.h +++ b/libringbuffer/frontend_internal.h @@ -294,10 +294,10 @@ static inline void lib_ring_buffer_write_commit_counter(const struct lttng_ust_lib_ring_buffer_config *config, struct lttng_ust_lib_ring_buffer *buf, struct channel *chan, - unsigned long idx, unsigned long buf_offset, unsigned long commit_count, - struct lttng_ust_shm_handle *handle) + struct lttng_ust_shm_handle *handle, + struct commit_counters_hot *cc_hot) { unsigned long commit_seq_old; @@ -313,10 +313,9 @@ void lib_ring_buffer_write_commit_counter(const struct lttng_ust_lib_ring_buffer if (caa_unlikely(subbuf_offset(buf_offset - commit_count, chan))) return; - commit_seq_old = v_read(config, &shmp_index(handle, buf->commit_hot, idx)->seq); + commit_seq_old = v_read(config, &cc_hot->seq); if (caa_likely((long) (commit_seq_old - commit_count) < 0)) - v_set(config, &shmp_index(handle, buf->commit_hot, idx)->seq, - commit_count); + v_set(config, &cc_hot->seq, commit_count); } extern int lib_ring_buffer_create(struct lttng_ust_lib_ring_buffer *buf, diff --git a/libringbuffer/ring_buffer_frontend.c b/libringbuffer/ring_buffer_frontend.c index 1396f44a..accd5dc5 100644 --- a/libringbuffer/ring_buffer_frontend.c +++ b/libringbuffer/ring_buffer_frontend.c @@ -1623,9 +1623,10 @@ void lib_ring_buffer_switch_old_start(struct lttng_ust_lib_ring_buffer *buf, /* Check if the written buffer has to be delivered */ lib_ring_buffer_check_deliver(config, buf, chan, offsets->old, commit_count, oldidx, handle, tsc); - lib_ring_buffer_write_commit_counter(config, buf, chan, oldidx, + lib_ring_buffer_write_commit_counter(config, buf, chan, offsets->old + config->cb.subbuffer_header_size(), - commit_count, handle); + commit_count, handle, + shmp_index(handle, buf->commit_hot, oldidx)); } /* @@ -1661,8 +1662,9 @@ void lib_ring_buffer_switch_old_end(struct lttng_ust_lib_ring_buffer *buf, commit_count = v_read(config, &shmp_index(handle, buf->commit_hot, oldidx)->cc); lib_ring_buffer_check_deliver(config, buf, chan, offsets->old - 1, commit_count, oldidx, handle, tsc); - lib_ring_buffer_write_commit_counter(config, buf, chan, oldidx, - offsets->old + padding_size, commit_count, handle); + lib_ring_buffer_write_commit_counter(config, buf, chan, + offsets->old + padding_size, commit_count, handle, + shmp_index(handle, buf->commit_hot, oldidx)); } /* @@ -1696,9 +1698,10 @@ void lib_ring_buffer_switch_new_start(struct lttng_ust_lib_ring_buffer *buf, /* Check if the written buffer has to be delivered */ lib_ring_buffer_check_deliver(config, buf, chan, offsets->begin, commit_count, beginidx, handle, tsc); - lib_ring_buffer_write_commit_counter(config, buf, chan, beginidx, + lib_ring_buffer_write_commit_counter(config, buf, chan, offsets->begin + config->cb.subbuffer_header_size(), - commit_count, handle); + commit_count, handle, + shmp_index(handle, buf->commit_hot, beginidx)); } /*