Currently, the dirty-sync-missed-zero-copy stat is incremented only when an entire batch of IO operations fails to use zerocopy and falls back to a normal copy. As long as at least one IO in the batch is successfully zero-copied, the whole batch is treated as a success. This hides individual IO fallbacks and makes the migration stat less accurate than it could be.
Make the stat more accurate by reporting at a finer granularity, i.e, by incrementing for every individual IO fallback that occurs. Suggested-by: Peter Xu <[email protected]> Signed-off-by: Tejus GK <[email protected]> --- include/io/channel-socket.h | 6 +----- include/io/channel.h | 5 ++--- io/channel-socket.c | 13 ++++--------- migration/multifd.c | 8 +++++--- qapi/migration.json | 3 +-- 5 files changed, 13 insertions(+), 22 deletions(-) diff --git a/include/io/channel-socket.h b/include/io/channel-socket.h index a1ef3136ea..5c5714668e 100644 --- a/include/io/channel-socket.h +++ b/include/io/channel-socket.h @@ -50,11 +50,7 @@ struct QIOChannelSocket { ssize_t zero_copy_queued; ssize_t zero_copy_sent; bool blocking; - /** - * This flag indicates whether any new data was successfully sent with - * zerocopy since the last qio_channel_socket_flush() call. - */ - bool new_zero_copy_sent_success; + ssize_t zero_copy_fallback; }; diff --git a/include/io/channel.h b/include/io/channel.h index 1b02350437..70f701ae16 100644 --- a/include/io/channel.h +++ b/include/io/channel.h @@ -1013,9 +1013,8 @@ int coroutine_mixed_fn qio_channel_writev_full_all(QIOChannel *ioc, * * If not implemented, acts as a no-op, and returns 0. * - * Returns -1 if any error is found, - * 1 if every send failed to use zero copy. - * 0 otherwise. + * Returns -1 if any error is found, otherwise returns a non-negative number + * indicating the number of IO requests that fell back to copy. */ int qio_channel_flush(QIOChannel *ioc, diff --git a/io/channel-socket.c b/io/channel-socket.c index 3053b35ad8..08b9862074 100644 --- a/io/channel-socket.c +++ b/io/channel-socket.c @@ -72,7 +72,7 @@ qio_channel_socket_new(void) sioc->zero_copy_queued = 0; sioc->zero_copy_sent = 0; sioc->blocking = false; - sioc->new_zero_copy_sent_success = false; + sioc->zero_copy_fallback = 0; ioc = QIO_CHANNEL(sioc); qio_channel_set_feature(ioc, QIO_CHANNEL_FEATURE_SHUTDOWN); @@ -881,8 +881,8 @@ static int qio_channel_socket_flush_internal(QIOChannel *ioc, sioc->zero_copy_sent += serr->ee_data - serr->ee_info + 1; /* If any sendmsg() succeeded using zero copy, mark zerocopy success */ - if (serr->ee_code != SO_EE_CODE_ZEROCOPY_COPIED) { - sioc->new_zero_copy_sent_success = true; + if (serr->ee_code == SO_EE_CODE_ZEROCOPY_COPIED) { + sioc->zero_copy_fallback++; } } @@ -900,12 +900,7 @@ static int qio_channel_socket_flush(QIOChannel *ioc, return ret; } - if (sioc->new_zero_copy_sent_success) { - sioc->new_zero_copy_sent_success = false; - return 0; - } - - return 1; + return sioc->zero_copy_fallback; } #endif /* QEMU_MSG_ZEROCOPY */ diff --git a/migration/multifd.c b/migration/multifd.c index ad6261688f..726e40903d 100644 --- a/migration/multifd.c +++ b/migration/multifd.c @@ -593,7 +593,7 @@ void multifd_send_shutdown(void) static int multifd_zero_copy_flush(QIOChannel *c) { - int ret; + ssize_t ret; Error *err = NULL; ret = qio_channel_flush(c, &err); @@ -601,8 +601,10 @@ static int multifd_zero_copy_flush(QIOChannel *c) error_report_err(err); return -1; } - if (ret == 1) { - qatomic_add(&mig_stats.dirty_sync_missed_zero_copy, 1); + + if (qatomic_read(&mig_stats.dirty_sync_missed_zero_copy) != (uint64_t)ret) { + /* Update statistics if more fallback detected */ + qatomic_set(&mig_stats.dirty_sync_missed_zero_copy, (uint64_t)ret); } return ret; diff --git a/qapi/migration.json b/qapi/migration.json index f925e5541b..94977b8810 100644 --- a/qapi/migration.json +++ b/qapi/migration.json @@ -58,8 +58,7 @@ # (since 7.0). # # @dirty-sync-missed-zero-copy: Number of times dirty RAM -# synchronization could not avoid copying dirty pages. This is -# between 0 and @dirty-sync-count * @multifd-channels. +# synchronization could not avoid copying dirty pages. # (since 7.1) # # Since: 0.14 -- 2.43.7
