On 4/12/07, Jeff Moyer <[email protected]> wrote:
I didn't see any response to Zach's request for code that actually
tests out the shared ring buffer. Do you have such code?
Yes, I do. I was stress testing the code since last night. After 20+
hours of stress run with fio and aio-stress, now I'm posting it with
confidence.
I modified libaio's io_getevents to take advantage of new user level
reap function. The feature is exported out via ring->compat_features.
btw, is compat_feature suppose to be a version number or a bit mask?
I think bitmask make more sense and more flexible.
(warning: some lines are extremely long in the patch and my email
client will probably mangle it badly).
diff -Nurp libaio-0.3.104/src/io_getevents.c
libaio-0.3.104-new/src/io_getevents.c
--- libaio-0.3.104/src/io_getevents.c 2003-06-18 12:58:21.000000000 -0700
+++ libaio-0.3.104-new/src/io_getevents.c 2007-04-12 17:35:06.000000000 -0700
@@ -21,10 +21,13 @@
#include <stdlib.h>
#include <time.h>
#include "syscall.h"
+#include <asm/system.h>
io_syscall5(int, __io_getevents_0_4, io_getevents, io_context_t, ctx,
long, min_nr, long, nr, struct io_event *, events, struct timespec *,
timeout)
#define AIO_RING_MAGIC 0xa10a10a1
+#define AIO_RING_BASE 1
+#define AIO_RING_USER_REAP 2
/* Ben will hate me for this */
struct aio_ring {
@@ -41,7 +44,11 @@ struct aio_ring {
int io_getevents_0_4(io_context_t ctx, long min_nr, long nr, struct
io_event * events, struct timespec * timeout)
{
+ long i = 0, ret;
+ unsigned head;
+ struct io_event *evt_base;
struct aio_ring *ring;
+
ring = (struct aio_ring*)ctx;
if (ring==NULL || ring->magic != AIO_RING_MAGIC)
goto do_syscall;
@@ -49,9 +56,35 @@ int io_getevents_0_4(io_context_t ctx, l
if (ring->head == ring->tail)
return 0;
}
-
+
+ if (!(ring->compat_features & AIO_RING_USER_REAP))
+ goto do_syscall;
+
+ if (min_nr > nr || min_nr < 0 || nr < 0)
+ return -EINVAL;
+
+ evt_base = (struct io_event *) (ring + 1);
+ while (i < nr) {
+ head = ring->head;
+ if (head == ring->tail)
+ break;
+
+ *events = evt_base[head & (ring->nr - 1)];
+ if (head == cmpxchg(&ring->head, head, head + 1)) {
+ events++;
+ i++;
+ }
+ }
+
+ if (i >= min_nr)
+ return i;
+
do_syscall:
- return __io_getevents_0_4(ctx, min_nr, nr, events, timeout);
+ ret = __io_getevents_0_4(ctx, min_nr - i, nr - i, events, timeout);
+ if (ret >= 0)
+ return i + ret;
+ else
+ return i ? i : ret;
}
DEFSYMVER(io_getevents_0_4, io_getevents, 0.4)
-
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