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Implement an fd pool to get real AIO with posix-aio

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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
This commit is contained in:
aliguori 2008-09-26 15:59:29 +00:00
parent 997306fc22
commit 5353872545
1 changed files with 65 additions and 3 deletions
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68
block-raw-posix.c
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@ -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) {