On Thu, Aug 1, 2024 at 1:30 PM Zijian Zhang <zijianzhang@xxxxxxxxxxxxx> wrote:
>
> On 7/31/24 3:32 PM, Willem de Bruijn wrote:
> > zijianzhang@ wrote:
> >> From: Zijian Zhang <zijianzhang@xxxxxxxxxxxxx>
> >>
> >> We update selftests/net/msg_zerocopy.c to accommodate the new mechanism,
>
> First of all, thanks for the detailed suggestions!
>
> >
> > 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.
> >
>
> Agreed.
>
> >> 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 <zijianzhang@xxxxxxxxxxxxx>
> >> Signed-off-by: Xiaochun Lu <xiaochun.lu@xxxxxxxxxxxxx>
> >
> >> -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.
> >
>
> Ack.
>
> >> + 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?
> >
>
> Yes, the same msg_control will be reused.
>
> The overall paradiagm is,
> start:
> sendmsg(..)
> sendmsg(..)
> ... sends_since_notify sendmsgs in total
>
> add_zcopy_info(..)
> sendmsg(.., msg_control)
> do_recv_completions_sendmsg(..)
> goto start;
>
> if (sends_since_notify + 1 >= cfg_notification_limit), add_zcopy_info
> will be invoked, and the right next sendmsg will have the msg_control
> passed in.
>
> If (added_zcopy_info), do_recv_completions_sendmsg will be invoked,
> and added_zcopy_info will be set to false in it.
This does not seem like it would need a global variable?
> >> +}
> >> +
> >> +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.
> >
>
> Ack.
>
> >> +{
> >> + 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.
> >
>
> -Z is more clear, and the hybrid testcase will be helpful.
>
> Btw, before I put some efforts to solve the current issues, I think
> I should wait for comments about api change from linux-api@xxxxxxxxxxxxxxx?
I'm not sure whether anyone on that list will give feedback.
I would continue with revisions at a normal schedule, as long as that
stays in the Cc.
