+ Dave Miller, Jakub Kicinski, Paolo Abeni, Shuah Khan,
linux-kselftest@xxxxxxxxxxxxxxx
On Mon, Jul 08, 2024 at 09:04:05PM +0000, zijianzhang@xxxxxxxxxxxxx wrote:
> From: Zijian Zhang <zijianzhang@xxxxxxxxxxxxx>
>
> We update selftests/net/msg_zerocopy.c to accommodate the new mechanism,
> 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 context of selftest, notifications of TCP are more likely to
> 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>
> ---
> tools/testing/selftests/net/msg_zerocopy.c | 111 ++++++++++++++++++--
> tools/testing/selftests/net/msg_zerocopy.sh | 1 +
> 2 files changed, 105 insertions(+), 7 deletions(-)
>
> diff --git a/tools/testing/selftests/net/msg_zerocopy.c b/tools/testing/selftests/net/msg_zerocopy.c
...
> @@ -466,6 +504,44 @@ static void do_recv_completions(int fd, int domain)
> sends_since_notify = 0;
> }
>
> +static void do_recv_completions2(void)
> +{
> + 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;
> + }
nit: If any arms of a conditional have {}, then all arms should have them
> +
> + completions += range;
> +
> + if (cfg_verbose >= 2)
> + fprintf(stderr, "completed: %u (h=%u l=%u)\n",
> + range, hi, lo);
> + }
> +
> + sends_since_notify = 0;
> + added_zcopy_info = false;
> +}
...
