Stephen C. Tweedie
2006-Sep-28 22:25 UTC
[Xen-devel] [Patch] Remove timeout in blktap''s main tapdisk select loop
tapdisk was using a 1msec select() timeout in its main event loop. On
timeout, the loop does nothing except repeat, so the timeout achieves
nothing; worse, on a machine with HZ set to less than 1000, a msec
timeout returns immediately, sending tapdisk into a 100%-CPU-
utilisation loop.
Simply remove the timeout entirely; everything still works fine, and
much more efficiently when idle.
Signed-off-by: Stephen Tweedie <sct@redhat.com>
diff -r aeba3dd98fbb -r 49d429529228 tools/blktap/drivers/tapdisk.c
--- a/tools/blktap/drivers/tapdisk.c Thu Sep 28 18:05:08 2006 +0100
+++ b/tools/blktap/drivers/tapdisk.c Thu Sep 28 23:24:43 2006 +0100
@@ -271,7 +271,6 @@ static int read_msg(char *buf)
int length, len, msglen, tap_fd, *io_fd;
char *ptr, *path;
image_t *img;
- struct timeval timeout;
msg_hdr_t *msg;
msg_newdev_t *msg_dev;
msg_pid_t *msg_pid;
@@ -579,8 +578,7 @@ int main(int argc, char *argv[])
{
int len, msglen, ret;
char *p, *buf;
- fd_set readfds, writefds;
- struct timeval timeout;
+ fd_set readfds, writefds;
fd_list_entry_t *ptr;
struct tap_disk *drv;
struct td_state *s;
@@ -622,12 +620,9 @@ int main(int argc, char *argv[])
/*Set all tap fds*/
LOCAL_FD_SET(&readfds);
- timeout.tv_sec = 0;
- timeout.tv_usec = 1000;
-
/*Wait for incoming messages*/
ret = select(maxfds + 1, &readfds, (fd_set *) 0,
- (fd_set *) 0, &timeout);
+ (fd_set *) 0, NULL);
if (ret > 0)
{
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