With the kernel's zerocopy notification mechanism, the caller can determine whether * All syscalls successfully used zero copy * At least one syscall failed to use zero copy
But, as of now QEMU's IO channel flush function semantics are like * 1 => all syscalls failed to use zero copy * 0 => at least one syscall successfully used zero copy This is not aligned with what the kernel reports, and ends up reporting false negatives for cases like when there's just a single successful zerocopy amongst a collection of deferred zero-copies during a flush. Fix this by inverting the return semantics of the IO flush function. Suggested-by: Peter Xu <[email protected]> Suggested-by: Daniel P. Berrangé <[email protected]> Signed-off-by: Tejus GK <[email protected]> --- include/io/channel-socket.h | 6 +----- include/io/channel.h | 4 ++-- io/channel-socket.c | 16 ++++++++-------- 3 files changed, 11 insertions(+), 15 deletions(-) diff --git a/include/io/channel-socket.h b/include/io/channel-socket.h index a1ef3136ea..b07cd61477 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; + bool zero_copy_fallback; }; diff --git a/include/io/channel.h b/include/io/channel.h index 1b02350437..c357da5460 100644 --- a/include/io/channel.h +++ b/include/io/channel.h @@ -1014,8 +1014,8 @@ 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. + * 1 if at least one send failed to use zero copy. + * 0 if every send successfully used zero copy. */ int qio_channel_flush(QIOChannel *ioc, diff --git a/io/channel-socket.c b/io/channel-socket.c index 3053b35ad8..ea2ec84108 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 = false; ioc = QIO_CHANNEL(sioc); qio_channel_set_feature(ioc, QIO_CHANNEL_FEATURE_SHUTDOWN); @@ -880,9 +880,9 @@ static int qio_channel_socket_flush_internal(QIOChannel *ioc, /* No errors, count successfully finished sendmsg()*/ 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) { + /* If any sendmsg() fell back to a copy, mark fallback as true */ + sioc->zero_copy_fallback = true; } } @@ -900,12 +900,12 @@ 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; + if (sioc->zero_copy_fallback) { + sioc->zero_copy_fallback = false; + return 1; } - return 1; + return 0; } #endif /* QEMU_MSG_ZEROCOPY */ -- 2.43.7
