[S] Change in libosmocore[master]: HACK: Allow io_uring_submit batching just ahead of poll

[laforge]

laforge has uploaded this change for review. ( 
https://gerrit.osmocom.org/c/libosmocore/+/36364?usp=email )


Change subject: HACK: Allow io_uring_submit batching just ahead of poll
......................................................................

HACK: Allow io_uring_submit batching just ahead of poll

Let's add a mode (enabled via the LIBOSMO_IO_URING_BATCH environment
variable), where we don't call io_uring_submit() after every operation
we add to the submission queue.  Rather, do that once before we go into
poll.

This should massively reduce the amount of io_uring_enter() syscalls
we're seeing.

Change-Id: Ia27ada909df246f21d110d8ae0b40229aacd579d
---
M src/core/osmo_io_uring.c
M src/core/select.c
2 files changed, 35 insertions(+), 2 deletions(-)



  git pull ssh://gerrit.osmocom.org:29418/libosmocore refs/changes/64/36364/1

diff --git a/src/core/osmo_io_uring.c b/src/core/osmo_io_uring.c
index 569f150..6801eb4 100644
--- a/src/core/osmo_io_uring.c
+++ b/src/core/osmo_io_uring.c
@@ -60,6 +60,7 @@
 };

 static __thread struct osmo_io_uring g_ring;
+static bool g_batch = false;

 static void iofd_uring_cqe(struct io_uring *ring);

@@ -90,6 +91,9 @@
 {
        int rc, evfd;

+       if (getenv("LIBOSMO_IO_URING_BATCH"))
+               g_batch = true;
+
        rc = io_uring_queue_init(IOFD_URING_ENTRIES, &g_ring.ring, 0);
        if (rc < 0)
                osmo_panic("failure during io_uring_queue_init(): %s\n", 
strerror(-rc));
@@ -175,7 +179,8 @@
        }
        io_uring_sqe_set_data(sqe, msghdr);

-       io_uring_submit(&g_ring.ring);
+       if (!g_batch)
+               io_uring_submit(&g_ring.ring);
        /* NOTE: This only works if we have one read per fd */
        iofd->u.uring.read_msghdr = msghdr;
 }
@@ -315,7 +320,8 @@
                OSMO_ASSERT(0);
        }

-       io_uring_submit(&g_ring.ring);
+       if (!g_batch)
+               io_uring_submit(&g_ring.ring);
        iofd->u.uring.write_msghdr = msghdr;

        return 0;
@@ -529,4 +535,10 @@
        .notify_connected = iofd_uring_notify_connected,
 };

+void osmo_io_uring_submit(void)
+{
+       if (g_batch)
+               io_uring_submit(&g_ring.ring);
+}
+
 #endif /* defined(__linux__) */
diff --git a/src/core/select.c b/src/core/select.c
index 70047f0..0a4302f 100644
--- a/src/core/select.c
+++ b/src/core/select.c
@@ -426,12 +426,16 @@
        return work;
 }

+void osmo_io_uring_submit(void);
+
 static int _osmo_select_main(int polling)
 {
        unsigned int n_poll;
        int rc;
        int timeout = 0;

+       osmo_io_uring_submit();
+
        /* prepare read and write fdsets */
        n_poll = poll_fill_fds();


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Gerrit-Project: libosmocore
Gerrit-Branch: master
Gerrit-Change-Id: Ia27ada909df246f21d110d8ae0b40229aacd579d
Gerrit-Change-Number: 36364
Gerrit-PatchSet: 1
Gerrit-Owner: laforge <lafo...@osmocom.org>
Gerrit-MessageType: newchange