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authoraliguori <aliguori@c046a42c-6fe2-441c-8c8c-71466251a162>2008-09-26 15:59:29 +0000
committeraliguori <aliguori@c046a42c-6fe2-441c-8c8c-71466251a162>2008-09-26 15:59:29 +0000
commit5353872545861d8d21bf9fcc64a25cbfc8cd2eac (patch)
treee33448006dbfd0c24d1580f28b83cac1c6d17ec2 /block-raw-posix.c
parent997306fc2246048b9a4e8df4b4bb96eab6c65a82 (diff)
Implement an fd pool to get real AIO with posix-aio
This patch implements a simple fd pool to allow many AIO requests with posix-aio. The result is significantly improved performance (identical to that reported for linux-aio) for both cache=on and cache=off. The fundamental problem with posix-aio is that it limits itself to one thread per-file descriptor. I don't know why this is, but this patch provides a simple mechanism to work around this (duplicating the file descriptor). This isn't a great solution, but it seems like a reasonable intermediate step between posix-aio and a custom thread-pool to replace it. Ryan Harper will be posting some performance analysis he did comparing posix-aio with fd pooling against linux-aio. The size of the posix-aio thread pool and the fd pool were largely determined by him based on this analysis. Signed-off-by: Anthony Liguori <aliguori@us.ibm.com> git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5323 c046a42c-6fe2-441c-8c8c-71466251a162
Diffstat (limited to 'block-raw-posix.c')
-rw-r--r--block-raw-posix.c68
1 files changed, 65 insertions, 3 deletions
diff --git a/block-raw-posix.c b/block-raw-posix.c
index 147730dd73..c469241853 100644
--- a/block-raw-posix.c
+++ b/block-raw-posix.c
@@ -84,10 +84,16 @@
reopen it to see if the disk has been changed */
#define FD_OPEN_TIMEOUT 1000
+/* posix-aio doesn't allow multiple outstanding requests to a single file
+ * descriptor. we implement a pool of dup()'d file descriptors to work
+ * around this */
+#define RAW_FD_POOL_SIZE 64
+
typedef struct BDRVRawState {
int fd;
int type;
unsigned int lseek_err_cnt;
+ int fd_pool[RAW_FD_POOL_SIZE];
#if defined(__linux__)
/* linux floppy specific */
int fd_open_flags;
@@ -109,6 +115,7 @@ static int raw_open(BlockDriverState *bs, const char *filename, int flags)
{
BDRVRawState *s = bs->opaque;
int fd, open_flags, ret;
+ int i;
posix_aio_init();
@@ -138,6 +145,8 @@ static int raw_open(BlockDriverState *bs, const char *filename, int flags)
return ret;
}
s->fd = fd;
+ for (i = 0; i < RAW_FD_POOL_SIZE; i++)
+ s->fd_pool[i] = -1;
#if defined(O_DIRECT)
s->aligned_buf = NULL;
if (flags & BDRV_O_DIRECT) {
@@ -436,6 +445,7 @@ static int raw_pwrite(BlockDriverState *bs, int64_t offset,
typedef struct RawAIOCB {
BlockDriverAIOCB common;
+ int fd;
struct aiocb aiocb;
struct RawAIOCB *next;
int ret;
@@ -447,6 +457,38 @@ typedef struct PosixAioState
RawAIOCB *first_aio;
} PosixAioState;
+static int raw_fd_pool_get(BDRVRawState *s)
+{
+ int i;
+
+ for (i = 0; i < RAW_FD_POOL_SIZE; i++) {
+ /* already in use */
+ if (s->fd_pool[i] != -1)
+ continue;
+
+ /* try to dup file descriptor */
+ s->fd_pool[i] = dup(s->fd);
+ if (s->fd_pool[i] != -1)
+ return s->fd_pool[i];
+ }
+
+ /* we couldn't dup the file descriptor so just use the main one */
+ return s->fd;
+}
+
+static void raw_fd_pool_put(RawAIOCB *acb)
+{
+ BDRVRawState *s = acb->common.bs->opaque;
+ int i;
+
+ for (i = 0; i < RAW_FD_POOL_SIZE; i++) {
+ if (s->fd_pool[i] == acb->fd) {
+ close(s->fd_pool[i]);
+ s->fd_pool[i] = -1;
+ }
+ }
+}
+
static void posix_aio_read(void *opaque)
{
PosixAioState *s = opaque;
@@ -487,6 +529,7 @@ static void posix_aio_read(void *opaque)
if (ret == ECANCELED) {
/* remove the request */
*pacb = acb->next;
+ raw_fd_pool_put(acb);
qemu_aio_release(acb);
} else if (ret != EINPROGRESS) {
/* end of aio */
@@ -503,6 +546,7 @@ static void posix_aio_read(void *opaque)
*pacb = acb->next;
/* call the callback */
acb->common.cb(acb->common.opaque, ret);
+ raw_fd_pool_put(acb);
qemu_aio_release(acb);
break;
} else {
@@ -577,7 +621,8 @@ static RawAIOCB *raw_aio_setup(BlockDriverState *bs,
acb = qemu_aio_get(bs, cb, opaque);
if (!acb)
return NULL;
- acb->aiocb.aio_fildes = s->fd;
+ acb->fd = raw_fd_pool_get(s);
+ acb->aiocb.aio_fildes = acb->fd;
acb->aiocb.aio_sigevent.sigev_signo = SIGUSR2;
acb->aiocb.aio_sigevent.sigev_notify = SIGEV_SIGNAL;
acb->aiocb.aio_buf = buf;
@@ -684,6 +729,7 @@ static void raw_aio_cancel(BlockDriverAIOCB *blockacb)
break;
} else if (*pacb == acb) {
*pacb = acb->next;
+ raw_fd_pool_put(acb);
qemu_aio_release(acb);
break;
}
@@ -697,6 +743,18 @@ static int posix_aio_init(void)
}
#endif /* CONFIG_AIO */
+static void raw_close_fd_pool(BDRVRawState *s)
+{
+ int i;
+
+ for (i = 0; i < RAW_FD_POOL_SIZE; i++) {
+ if (s->fd_pool[i] != -1) {
+ close(s->fd_pool[i]);
+ s->fd_pool[i] = -1;
+ }
+ }
+}
+
static void raw_close(BlockDriverState *bs)
{
BDRVRawState *s = bs->opaque;
@@ -708,6 +766,7 @@ static void raw_close(BlockDriverState *bs)
qemu_free(s->aligned_buf);
#endif
}
+ raw_close_fd_pool(s);
}
static int raw_truncate(BlockDriverState *bs, int64_t offset)
@@ -898,7 +957,7 @@ kern_return_t GetBSDPath( io_iterator_t mediaIterator, char *bsdPath, CFIndex ma
static int hdev_open(BlockDriverState *bs, const char *filename, int flags)
{
BDRVRawState *s = bs->opaque;
- int fd, open_flags, ret;
+ int fd, open_flags, ret, i;
posix_aio_init();
@@ -963,6 +1022,8 @@ static int hdev_open(BlockDriverState *bs, const char *filename, int flags)
return ret;
}
s->fd = fd;
+ for (i = 0; i < RAW_FD_POOL_SIZE; i++)
+ s->fd_pool[i] = -1;
#if defined(__linux__)
/* close fd so that we can reopen it as needed */
if (s->type == FTYPE_FD) {
@@ -975,7 +1036,6 @@ static int hdev_open(BlockDriverState *bs, const char *filename, int flags)
}
#if defined(__linux__)
-
/* Note: we do not have a reliable method to detect if the floppy is
present. The current method is to try to open the floppy at every
I/O and to keep it opened during a few hundreds of ms. */
@@ -991,6 +1051,7 @@ static int fd_open(BlockDriverState *bs)
(qemu_get_clock(rt_clock) - s->fd_open_time) >= FD_OPEN_TIMEOUT) {
close(s->fd);
s->fd = -1;
+ raw_close_fd_pool(s);
#ifdef DEBUG_FLOPPY
printf("Floppy closed\n");
#endif
@@ -1091,6 +1152,7 @@ static int raw_eject(BlockDriverState *bs, int eject_flag)
if (s->fd >= 0) {
close(s->fd);
s->fd = -1;
+ raw_close_fd_pool(s);
}
fd = open(bs->filename, s->fd_open_flags | O_NONBLOCK);
if (fd >= 0) {