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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] Switch from select() to poll() in xenconsoled's IO loop
Just to be clear, this is version 5 of the patch.
Git send-email mysteriously dropped my subject prefix.
Wei.
On Tue, 2013-01-08 at 11:50 +0000, Wei Liu wrote:
> In Linux select() typically supports up to 1024 file descriptors. This can be
> a problem when user tries to boot up many guests. Switching to poll() has
> minimum impact on existing code and has better scalibility.
>
> pollfd array is dynamically allocated / reallocated. If the array fails to
> expand, we just ignore the incoming fd.
>
> Change from V2:
> * remove unnecessary malloc in initialize_pollfd_arrays
> * use ROUND_UP to get new size of arrays
>
> Change from V3:
> * remove initialize and destroy function for array
> * embedded tracking structure in struct domain, eliminate fd_to_pollfd
>
> Change from V4:
> * make xs_pollfd local to io.c
> * add back the 5 ms fuzz
> * handle POLLERR and POLLHUP
> * treat POLLPRI as error if set in revents
> * abort if xenconsoled's own fds get screwed
> * handle broken tty if tty's fds get screwed
>
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
> tools/console/daemon/io.c | 189
> +++++++++++++++++++++++++++++++--------------
> 1 file changed, 131 insertions(+), 58 deletions(-)
>
> diff --git a/tools/console/daemon/io.c b/tools/console/daemon/io.c
> index 48fe151..8d16cac 100644
> --- a/tools/console/daemon/io.c
> +++ b/tools/console/daemon/io.c
> @@ -28,7 +28,7 @@
> #include <stdlib.h>
> #include <errno.h>
> #include <string.h>
> -#include <sys/select.h>
> +#include <poll.h>
> #include <fcntl.h>
> #include <unistd.h>
> #include <termios.h>
> @@ -69,6 +69,7 @@ static int log_hv_fd = -1;
> static evtchn_port_or_error_t log_hv_evtchn = -1;
> static xc_interface *xch; /* why does xenconsoled have two xc handles ? */
> static xc_evtchn *xce_handle = NULL;
> +static struct pollfd *xce_pollfd = NULL;
>
> struct buffer {
> char *data;
> @@ -81,7 +82,9 @@ struct buffer {
> struct domain {
> int domid;
> int master_fd;
> + struct pollfd *master_pollfd;
> int slave_fd;
> + struct pollfd *slave_pollfd;
> int log_fd;
> bool is_dead;
> unsigned last_seen;
> @@ -92,6 +95,7 @@ struct domain {
> evtchn_port_or_error_t local_port;
> evtchn_port_or_error_t remote_port;
> xc_evtchn *xce_handle;
> + struct pollfd *xce_pollfd;
> struct xencons_interface *interface;
> int event_count;
> long long next_period;
> @@ -769,6 +773,17 @@ static int ring_free_bytes(struct domain *dom)
> return (sizeof(intf->in) - space);
> }
>
> +static void domain_handle_broken_tty(struct domain *dom, int recreate)
> +{
> + domain_close_tty(dom);
> +
> + if (recreate) {
> + domain_create_tty(dom);
> + } else {
> + shutdown_domain(dom);
> + }
> +}
> +
> static void handle_tty_read(struct domain *dom)
> {
> ssize_t len = 0;
> @@ -794,13 +809,7 @@ static void handle_tty_read(struct domain *dom)
> * keep the slave open for the duration.
> */
> if (len < 0) {
> - domain_close_tty(dom);
> -
> - if (domain_is_valid(dom->domid)) {
> - domain_create_tty(dom);
> - } else {
> - shutdown_domain(dom);
> - }
> + domain_handle_broken_tty(dom, domain_is_valid(dom->domid));
> } else if (domain_is_valid(dom->domid)) {
> prod = intf->in_prod;
> for (i = 0; i < len; i++) {
> @@ -828,14 +837,7 @@ static void handle_tty_write(struct domain *dom)
> if (len < 1) {
> dolog(LOG_DEBUG, "Write failed on domain %d: %zd, %d\n",
> dom->domid, len, errno);
> -
> - domain_close_tty(dom);
> -
> - if (domain_is_valid(dom->domid)) {
> - domain_create_tty(dom);
> - } else {
> - shutdown_domain(dom);
> - }
> + domain_handle_broken_tty(dom, domain_is_valid(dom->domid));
> } else {
> buffer_advance(&dom->buffer, len);
> }
> @@ -928,9 +930,53 @@ static void handle_log_reload(void)
> }
> }
>
> +struct pollfd *xs_pollfd;
> +static struct pollfd *fds;
> +static unsigned int current_array_size;
> +static unsigned int nr_fds;
> +
> +#define ROUNDUP(_x,_w) (((unsigned long)(_x)+(1UL<<(_w))-1) &
> ~((1UL<<(_w))-1))
> +static struct pollfd *set_fds(int fd, short events)
> +{
> + struct pollfd *ret;
> + if (current_array_size < nr_fds + 1) {
> + struct pollfd *new_fds = NULL;
> + unsigned long newsize;
> +
> + /* Round up to 2^8 boundary, in practice this just
> + * make newsize larger than current_array_size.
> + */
> + newsize = ROUNDUP(nr_fds + 1, 8);
> +
> + new_fds = realloc(fds, sizeof(struct pollfd)*newsize);
> + if (!new_fds)
> + goto fail;
> + fds = new_fds;
> +
> + memset(&fds[0] + current_array_size, 0,
> + sizeof(struct pollfd) * (newsize-current_array_size));
> + current_array_size = newsize;
> + }
> +
> + fds[nr_fds].fd = fd;
> + fds[nr_fds].events = events;
> + ret = &fds[nr_fds];
> + nr_fds++;
> +
> + return ret;
> +fail:
> + dolog(LOG_ERR, "realloc failed, ignoring fd %d\n", fd);
> + return NULL;
> +}
> +
> +static void reset_fds(void)
> +{
> + nr_fds = 0;
> + memset(fds, 0, sizeof(struct pollfd) * current_array_size);
> +}
> +
> void handle_io(void)
> {
> - fd_set readfds, writefds;
> int ret;
>
> if (log_hv) {
> @@ -959,21 +1005,17 @@ void handle_io(void)
>
> for (;;) {
> struct domain *d, *n;
> - int max_fd = -1;
> - struct timeval timeout;
> + int poll_timeout; /* timeout in milliseconds */
> struct timespec ts;
> long long now, next_timeout = 0;
>
> - FD_ZERO(&readfds);
> - FD_ZERO(&writefds);
> + reset_fds();
>
> - FD_SET(xs_fileno(xs), &readfds);
> - max_fd = MAX(xs_fileno(xs), max_fd);
> + xs_pollfd = set_fds(xs_fileno(xs), POLLIN|POLLPRI);
>
> - if (log_hv) {
> - FD_SET(xc_evtchn_fd(xce_handle), &readfds);
> - max_fd = MAX(xc_evtchn_fd(xce_handle), max_fd);
> - }
> + if (log_hv)
> + xce_pollfd = set_fds(xc_evtchn_fd(xce_handle),
> + POLLIN|POLLPRI);
>
> if (clock_gettime(CLOCK_MONOTONIC, &ts) < 0)
> return;
> @@ -982,10 +1024,12 @@ void handle_io(void)
> /* Re-calculate any event counter allowances & unblock
> domains with new allowance */
> for (d = dom_head; d; d = d->next) {
> - /* Add 5ms of fuzz since select() often returns
> - a couple of ms sooner than requested. Without
> - the fuzz we typically do an extra spin in select()
> - with a 1/2 ms timeout every other iteration */
> + /* CS 16257:955ee4fa1345 introduces a 5ms fuzz
> + * for select(), it is not clear poll() has
> + * similar behavior (returning a couple of ms
> + * sooner than requested) as well. Just leave
> + * the fuzz here. Remove it with a separate
> + * patch if necessary */
> if ((now+5) > d->next_period) {
> d->next_period = now + RATE_LIMIT_PERIOD;
> if (d->event_count >= RATE_LIMIT_ALLOWANCE) {
> @@ -1006,75 +1050,101 @@ void handle_io(void)
> !d->buffer.max_capacity ||
> d->buffer.size < d->buffer.max_capacity) {
> int evtchn_fd =
> xc_evtchn_fd(d->xce_handle);
> - FD_SET(evtchn_fd, &readfds);
> - max_fd = MAX(evtchn_fd, max_fd);
> + d->xce_pollfd = set_fds(evtchn_fd,
> + POLLIN|POLLPRI);
> }
> }
>
> if (d->master_fd != -1) {
> + short events = 0;
> if (!d->is_dead && ring_free_bytes(d))
> - FD_SET(d->master_fd, &readfds);
> + events |= POLLIN;
>
> if (!buffer_empty(&d->buffer))
> - FD_SET(d->master_fd, &writefds);
> - max_fd = MAX(d->master_fd, max_fd);
> + events |= POLLOUT;
> +
> + if (events)
> + d->master_pollfd =
> + set_fds(d->master_fd,
> + events|POLLPRI);
> }
> }
>
> /* If any domain has been rate limited, we need to work
> - out what timeout to supply to select */
> + out what timeout to supply to poll */
> if (next_timeout) {
> long long duration = (next_timeout - now);
> if (duration <= 0) /* sanity check */
> duration = 1;
> - timeout.tv_sec = duration / 1000;
> - timeout.tv_usec = ((duration - (timeout.tv_sec * 1000))
> - * 1000);
> + poll_timeout = (int)duration;
> }
>
> - ret = select(max_fd + 1, &readfds, &writefds, 0,
> - next_timeout ? &timeout : NULL);
> + ret = poll(fds, nr_fds, next_timeout ? poll_timeout : -1);
>
> if (log_reload) {
> handle_log_reload();
> log_reload = 0;
> }
>
> - /* Abort if select failed, except for EINTR cases
> + /* Abort if poll failed, except for EINTR cases
> which indicate a possible log reload */
> if (ret == -1) {
> if (errno == EINTR)
> continue;
> - dolog(LOG_ERR, "Failure in select: %d (%s)",
> + dolog(LOG_ERR, "Failure in poll: %d (%s)",
> errno, strerror(errno));
> break;
> }
>
> - if (log_hv && FD_ISSET(xc_evtchn_fd(xce_handle), &readfds))
> - handle_hv_logs();
> + if (log_hv && xce_pollfd) {
> + if (xce_pollfd->revents & ~(POLLIN|POLLOUT|POLLPRI)) {
> + dolog(LOG_ERR,
> + "Failure in poll xce_handle: %d (%s)",
> + errno, strerror(errno));
> + break;
> + } else if (xce_pollfd->revents & POLLIN)
> + handle_hv_logs();
> + }
>
> if (ret <= 0)
> continue;
>
> - if (FD_ISSET(xs_fileno(xs), &readfds))
> - handle_xs();
> + if (xs_pollfd) {
> + if (xs_pollfd->revents & ~(POLLIN|POLLOUT|POLLPRI)) {
> + dolog(LOG_ERR,
> + "Failure in poll xs_handle: %d (%s)",
> + errno, strerror(errno));
> + break;
> + } else if (xs_pollfd->revents & POLLIN)
> + handle_xs();
> + }
>
> for (d = dom_head; d; d = n) {
> n = d->next;
> if (d->event_count < RATE_LIMIT_ALLOWANCE) {
> if (d->xce_handle != NULL &&
> - FD_ISSET(xc_evtchn_fd(d->xce_handle),
> - &readfds))
> - handle_ring_read(d);
> + d->xce_pollfd &&
> + !(d->xce_pollfd->revents &
> + ~(POLLIN|POLLOUT|POLLPRI)) &&
> + (d->xce_pollfd->revents &
> + POLLIN))
> + handle_ring_read(d);
> }
>
> - if (d->master_fd != -1 && FD_ISSET(d->master_fd,
> - &readfds))
> - handle_tty_read(d);
> -
> - if (d->master_fd != -1 && FD_ISSET(d->master_fd,
> - &writefds))
> - handle_tty_write(d);
> + if (d->master_fd != -1 && d->master_pollfd) {
> + if (d->master_pollfd->revents &
> + ~(POLLIN|POLLOUT|POLLPRI))
> + domain_handle_broken_tty(d,
> + domain_is_valid(d->domid));
> + else {
> + if (d->master_pollfd->revents &
> + POLLIN)
> + handle_tty_read(d);
> + if (d->master_pollfd->revents &
> + POLLOUT)
> + handle_tty_write(d);
> + }
> + }
>
> if (d->last_seen != enum_pass)
> shutdown_domain(d);
> @@ -1084,6 +1154,9 @@ void handle_io(void)
> }
> }
>
> + free(fds);
> + current_array_size = 0;
> +
> out:
> if (log_hv_fd != -1) {
> close(log_hv_fd);
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