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remove unneeded io_getevents syscall.

Vadim Fedorenko
January 06, 2019 04:42PM
# HG changeset patch
# User Vadim Fedorenko <vadimjunk@gmail.com>
# Date 1546810494 0
# Sun Jan 06 21:34:54 2019 +0000
# Node ID 3e538f6b8267d36f97b7dd67714c6ba0fba5e5bc
# Parent 6d15e452fa2eaf19408e24a0d0fcc3a31344a289
remove unneeded io_getevents syscall.

This work is based on cloudflare's work on optimization Linux AIO.
https://blog.cloudflare.com/io_submit-the-epoll-alternative-youve-never-heard-about/
The code is compilation of libaio library, it eliminates unnecessary
context-switch on getting new AIO events, doing all possible work in
userspace.

diff -r 6d15e452fa2e -r 3e538f6b8267 src/event/modules/ngx_epoll_module.c
--- a/src/event/modules/ngx_epoll_module.c Tue Dec 25 17:53:03 2018 +0300
+++ b/src/event/modules/ngx_epoll_module.c Sun Jan 06 21:34:54 2019 +0000
@@ -100,6 +100,35 @@
ngx_uint_t aio_requests;
} ngx_epoll_conf_t;

+#if (NGX_HAVE_FILE_AIO)
+
+/* Stolen from kernel arch/x86_64.h */
+#ifdef __x86_64__
+#define read_barrier() __asm__ __volatile__("lfence" ::: "memory")
+#else
+#ifdef __i386__
+#define read_barrier() __asm__ __volatile__("" : : : "memory")
+#else
+#define read_barrier() __sync_synchronize()
+#endif
+#endif
+
+/* Stolen from kernel fs/aio.c */
+#define AIO_RING_MAGIC 0xa10a10a1
+struct aio_ring {
+ unsigned id; /* kernel internal index number */
+ unsigned nr; /* number of io_events */
+ unsigned head;
+ unsigned tail;
+ unsigned magic;
+ unsigned compat_features;
+ unsigned incompat_features;
+ unsigned header_length; /* size of aio_ring */
+ struct io_event events[0];
+};
+
+#endif
+

static ngx_int_t ngx_epoll_init(ngx_cycle_t *cycle, ngx_msec_t timer);
#if (NGX_HAVE_EVENTFD)
@@ -241,6 +270,39 @@
io_getevents(aio_context_t ctx, long min_nr, long nr, struct io_event *events,
struct timespec *tmo)
{
+ /* Code based on cloudflare-blog */
+ ngx_int_t i = 0;
+
+ struct aio_ring *ring = (struct aio_ring *)ctx;
+ if (ring == NULL || ring->magic != AIO_RING_MAGIC) {
+ goto do_syscall;
+ }
+
+ while (i < nr) {
+ unsigned head = ring->head;
+ if (head == ring->tail) {
+ /* There are no more completions */
+ break;
+ } else {
+ /* There is another completion to reap */
+ events[i] = ring->events[head];
+ read_barrier();
+ ring->head = (head + 1) % ring->nr;
+ i++;
+ }
+ }
+
+ if (i == 0 && tmo != NULL && tmo->tv_sec == 0 &&
+ tmo->tv_nsec == 0) {
+ /* Requested non blocking operation. */
+ return 0;
+ }
+
+ if (i && i >= min_nr) {
+ return i;
+ }
+
+do_syscall:
return syscall(SYS_io_getevents, ctx, min_nr, nr, events, tmo);
}
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Subject Author Views Posted

remove unneeded io_getevents syscall.

Vadim Fedorenko 154 January 06, 2019 04:42PM

Re: remove unneeded io_getevents syscall.

Maxim Dounin 68 January 06, 2019 11:26PM



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