zijianzhang@ wrote: > From: Zijian Zhang <[email protected]> > > We update selftests/net/msg_zerocopy.c to accommodate the new mechanism,
Please make commit messages stand on their own. If someone does a git blame, make the message self explanatory. Replace "the new mechanism" with sendmsg SCM_ZC_NOTIFICATION. In patch 2 or as a separate patch 4, also add a new short section on this API in Documentation/networking/msg_zerocopy.rst. Probably with the same contents as a good explanation of the feature in the commit message of patch 2. > cfg_notification_limit has the same semantics for both methods. Test > results are as follows, we update skb_orphan_frags_rx to the same as > skb_orphan_frags to support zerocopy in the localhost test. > > cfg_notification_limit = 1, both method get notifications after 1 calling > of sendmsg. In this case, the new method has around 17% cpu savings in TCP > and 23% cpu savings in UDP. > +---------------------+---------+---------+---------+---------+ > | Test Type / Protocol| TCP v4 | TCP v6 | UDP v4 | UDP v6 | > +---------------------+---------+---------+---------+---------+ > | ZCopy (MB) | 7523 | 7706 | 7489 | 7304 | > +---------------------+---------+---------+---------+---------+ > | New ZCopy (MB) | 8834 | 8993 | 9053 | 9228 | > +---------------------+---------+---------+---------+---------+ > | New ZCopy / ZCopy | 117.42% | 116.70% | 120.88% | 126.34% | > +---------------------+---------+---------+---------+---------+ > > cfg_notification_limit = 32, both get notifications after 32 calling of > sendmsg, which means more chances to coalesce notifications, and less > overhead of poll + recvmsg for the original method. In this case, the new > method has around 7% cpu savings in TCP and slightly better cpu usage in > UDP. In the env of selftest, notifications of TCP are more likely to be > out of order than UDP, it's easier to coalesce more notifications in UDP. > The original method can get one notification with range of 32 in a recvmsg > most of the time. In TCP, most notifications' range is around 2, so the > original method needs around 16 recvmsgs to get notified in one round. > That's the reason for the "New ZCopy / ZCopy" diff in TCP and UDP here. > +---------------------+---------+---------+---------+---------+ > | Test Type / Protocol| TCP v4 | TCP v6 | UDP v4 | UDP v6 | > +---------------------+---------+---------+---------+---------+ > | ZCopy (MB) | 8842 | 8735 | 10072 | 9380 | > +---------------------+---------+---------+---------+---------+ > | New ZCopy (MB) | 9366 | 9477 | 10108 | 9385 | > +---------------------+---------+---------+---------+---------+ > | New ZCopy / ZCopy | 106.00% | 108.28% | 100.31% | 100.01% | > +---------------------+---------+---------+---------+---------+ > > In conclusion, when notification interval is small or notifications are > hard to be coalesced, the new mechanism is highly recommended. Otherwise, > the performance gain from the new mechanism is very limited. > > Signed-off-by: Zijian Zhang <[email protected]> > Signed-off-by: Xiaochun Lu <[email protected]> > -static bool do_sendmsg(int fd, struct msghdr *msg, bool do_zerocopy, int > domain) > +static void add_zcopy_info(struct msghdr *msg) > +{ > + struct zc_info *zc_info; > + struct cmsghdr *cm; > + > + if (!msg->msg_control) > + error(1, errno, "NULL user arg"); Don't add precondition checks for code entirely under your control. This is not a user API. > + cm = (struct cmsghdr *)msg->msg_control; > + cm->cmsg_len = CMSG_LEN(ZC_INFO_SIZE); > + cm->cmsg_level = SOL_SOCKET; > + cm->cmsg_type = SCM_ZC_NOTIFICATION; > + > + zc_info = (struct zc_info *)CMSG_DATA(cm); > + zc_info->size = ZC_NOTIFICATION_MAX; > + > + added_zcopy_info = true; Just initialize every time? Is this here to reuse the same msg_control as long as metadata is returned? > +} > + > +static bool do_sendmsg(int fd, struct msghdr *msg, > + enum notification_type do_zerocopy, int domain) > { > int ret, len, i, flags; > static uint32_t cookie; > @@ -200,6 +233,12 @@ static bool do_sendmsg(int fd, struct msghdr *msg, bool > do_zerocopy, int domain) > msg->msg_controllen = CMSG_SPACE(sizeof(cookie)); > msg->msg_control = (struct cmsghdr *)ckbuf; > add_zcopy_cookie(msg, ++cookie); > + } else if (do_zerocopy == MSG_ZEROCOPY_NOTIFY_SENDMSG && > + sends_since_notify + 1 >= cfg_notification_limit) { > + memset(&msg->msg_control, 0, sizeof(msg->msg_control)); > + msg->msg_controllen = CMSG_SPACE(ZC_INFO_SIZE); > + msg->msg_control = (struct cmsghdr *)zc_ckbuf; > + add_zcopy_info(msg); > } > } > > @@ -218,7 +257,7 @@ static bool do_sendmsg(int fd, struct msghdr *msg, bool > do_zerocopy, int domain) > if (do_zerocopy && ret) > expected_completions++; > } > - if (do_zerocopy && domain == PF_RDS) { > + if (msg->msg_control) { > msg->msg_control = NULL; > msg->msg_controllen = 0; > } > @@ -466,6 +505,44 @@ static void do_recv_completions(int fd, int domain) > sends_since_notify = 0; > } > > +static void do_recv_completions2(void) functionname2 is very uninformative. do_recv_completions_sendmsg or so. > +{ > + struct cmsghdr *cm = (struct cmsghdr *)zc_ckbuf; > + struct zc_info *zc_info; > + __u32 hi, lo, range; > + __u8 zerocopy; > + int i; > + > + zc_info = (struct zc_info *)CMSG_DATA(cm); > + for (i = 0; i < zc_info->size; i++) { > + hi = zc_info->arr[i].hi; > + lo = zc_info->arr[i].lo; > + zerocopy = zc_info->arr[i].zerocopy; > + range = hi - lo + 1; > + > + if (cfg_verbose && lo != next_completion) > + fprintf(stderr, "gap: %u..%u does not append to %u\n", > + lo, hi, next_completion); > + next_completion = hi + 1; > + > + if (zerocopied == -1) { > + zerocopied = zerocopy; > + } else if (zerocopied != zerocopy) { > + fprintf(stderr, "serr: inconsistent\n"); > + zerocopied = zerocopy; > + } > + > + completions += range; > + sends_since_notify -= range; > + > + if (cfg_verbose >= 2) > + fprintf(stderr, "completed: %u (h=%u l=%u)\n", > + range, hi, lo); > + } > + > + added_zcopy_info = false; > +} > + > /* Wait for all remaining completions on the errqueue */ > static void do_recv_remaining_completions(int fd, int domain) > { > @@ -553,11 +630,16 @@ static void do_tx(int domain, int type, int protocol) > else > do_sendmsg(fd, &msg, cfg_zerocopy, domain); > > - if (cfg_zerocopy && sends_since_notify >= > cfg_notification_limit) > + if (cfg_zerocopy == MSG_ZEROCOPY_NOTIFY_ERRQUEUE && > + sends_since_notify >= cfg_notification_limit) > do_recv_completions(fd, domain); > > + if (cfg_zerocopy == MSG_ZEROCOPY_NOTIFY_SENDMSG && > + added_zcopy_info) > + do_recv_completions2(); > + > while (!do_poll(fd, POLLOUT)) { > - if (cfg_zerocopy) > + if (cfg_zerocopy == MSG_ZEROCOPY_NOTIFY_ERRQUEUE) > do_recv_completions(fd, domain); > } > > @@ -715,7 +797,7 @@ static void parse_opts(int argc, char **argv) > > cfg_payload_len = max_payload_len; > > - while ((c = getopt(argc, argv, "46c:C:D:i:l:mp:rs:S:t:vz")) != -1) { > + while ((c = getopt(argc, argv, "46c:C:D:i:l:mnp:rs:S:t:vz")) != -1) { > switch (c) { > case '4': > if (cfg_family != PF_UNSPEC) > @@ -749,6 +831,9 @@ static void parse_opts(int argc, char **argv) > case 'm': > cfg_cork_mixed = true; > break; > + case 'n': > + cfg_zerocopy = MSG_ZEROCOPY_NOTIFY_SENDMSG; > + break; How about -Z to make clear that this is still MSG_ZEROCOPY, just with a different notification mechanism. And perhaps add a testcase that exercises both this mechanism and existing recvmsg MSG_ERRQUEUE. As they should work in parallel and concurrently in a multithreaded environment.
