+ Dave Miller, Jakub Kicinski, Paolo Abeni, Shuah Khan, linux-kselftest@vger.kernel.org

On Mon, Jul 08, 2024 at 09:04:05PM +0000, zijianzhang@bytedance.com wrote:

From: Zijian Zhang zijianzhang@bytedance.com

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@bytedance.com Signed-off-by: Xiaochun Lu xiaochun.lu@bytedance.com

---

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;

+}

...