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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] Switch to poll() in cxenstored's IO loop
On Tue, 2013-02-05 at 10:58 +0000, Ian Campbell wrote:
> On Tue, 2013-01-22 at 14:50 +0000, Wei Liu wrote:
> > > > > > + !(reopen_log_pipe0_pollfd->revents &
> > > > > > ~(POLLIN|POLLOUT|POLLPRI)) &&
> > > > >
> > > > > This represents an error case I think? Is there anything we can do
> > > > > about
> > > > > it? If this sort of error occurs and we do nothing will we end up just
> > > > > spinning because every subsequent poll will just return straight away?
> > > > >
> > > > >
> > > >
> > > > Yes, this represents an error. This indicates the pipe used to trigger
> > > > reopen_log is broken. What's the motivation of reopening log file?
> > >
> > > Rotation I should imagine.
> > >
> > > > I
> > > > have no idea about the use case. But simply ignoring this error instead
> > > > of crashing the process is better choice IMHO.
> > >
> > > Agreed, but my concern was that the daemon would spin consuming 100%
> > > CPU, which is nearly as bad as crashing.
> > >
> > > > The whole pollfd set is reinitialized for every loop. So it is also
> > > > possible that for the next loop it will success even previous poll
> > > > fails?
> > >
> > > I suppose it depends on the reason it failed. I would expect most of
> > > them would be pretty final rather than temporary but I haven't looked at
> > > the pipe docs.
> > >
> >
> > We can reinitialize the pipe if error occurs, because this pipe is only
> > used within xenstored itself to notify log reload.
>
> But if you get POLLPRI or POLLOUT you don't do this with the code as it
> currently stands (from the v2 patch):
> + if (reopen_log_pipe0_pollfd->revents &
> ~(POLLIN|POLLOUT|POLLPRI)) {
> + close(reopen_log_pipe[0]);
> + close(reopen_log_pipe[1]);
> + init_pipe(reopen_log_pipe);
> + } else if (reopen_log_pipe0_pollfd->revents & POLLIN)
> {
> + char c;
> + if (read(reopen_log_pipe[0], &c, 1) != 1)
> + barf_perror("read failed");
> + reopen_log();
> + }
>
> So on POLLRDHUP or POLLERR etc you reopen the log, on POLLIN you act as
> expected but for POLLPRI and POLLOUT you don't do anything.
>
> If these two events should never occur then you should include the in
> the error handling part of the above. If they can occur then you need to
> do something to handle them, otherwise they will just keep reoccuring on
> every iteration.
>
> The same goes for the other instances of this pattern.
>
> Ian.
>
I think POLLPRI and POLLOUT should not occur in most cases, here is a
updated version of the patch. Tested on my testbox and it works.
-----8<----
>From 22a7b50b8b0be62aeae7c86242a27dac1ffdb929 Mon Sep 17 00:00:00 2001
From: Wei Liu <wei.liu2@xxxxxxxxxx>
Date: Mon, 21 Jan 2013 19:07:37 +0000
Subject: [PATCH] Switch to poll() in cxenstored's IO loop
Poll() can support more file descriptors than select(). We've done this for
xenconsoled, now do this for cxenstored as well.
The code is taken from xenconsoled and modified to adapt to cxenstored.
Updated:
* reopen pipe if polling on reopen_log_pipe fails.
* exit if polling on some critical fds fails.
* clean up POLL*.
Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
tools/xenstore/xenstored_core.c | 171 ++++++++++++++++++++++++++-------------
tools/xenstore/xenstored_core.h | 2 +
2 files changed, 116 insertions(+), 57 deletions(-)
diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index bd44645..839e51d 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -19,7 +19,7 @@
#include <sys/types.h>
#include <sys/stat.h>
-#include <sys/select.h>
+#include <poll.h>
#ifndef NO_SOCKETS
#include <sys/socket.h>
#include <sys/un.h>
@@ -55,6 +55,12 @@
#include "hashtable.h"
extern xc_evtchn *xce_handle; /* in xenstored_domain.c */
+static struct pollfd *xce_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 bool verbose = false;
LIST_HEAD(connections);
@@ -62,6 +68,7 @@ static int tracefd = -1;
static bool recovery = true;
static bool remove_local = true;
static int reopen_log_pipe[2];
+static struct pollfd *reopen_log_pipe0_pollfd;
static char *tracefile = NULL;
static TDB_CONTEXT *tdb_ctx = NULL;
@@ -199,7 +206,7 @@ void trace_destroy(const void *data, const char *type)
/**
* Signal handler for SIGHUP, which requests that the trace log is reopened
* (in the main loop). A single byte is written to reopen_log_pipe, to awaken
- * the select() in the main loop.
+ * the poll() in the main loop.
*/
static void trigger_reopen_log(int signal __attribute__((unused)))
{
@@ -279,15 +286,12 @@ static int destroy_conn(void *_conn)
/* Flush outgoing if possible, but don't block. */
if (!conn->domain) {
- fd_set set;
- struct timeval none;
-
- FD_ZERO(&set);
- FD_SET(conn->fd, &set);
- none.tv_sec = none.tv_usec = 0;
+ struct pollfd pfd;
+ pfd.fd = conn->fd;
+ pfd.events = POLLOUT;
while (!list_empty(&conn->out_list)
- && select(conn->fd+1, NULL, &set, NULL, &none) == 1)
+ && poll(&pfd, 1, 0) == 1)
if (!write_messages(conn))
break;
close(conn->fd);
@@ -300,52 +304,74 @@ static int destroy_conn(void *_conn)
}
-static void set_fd(int fd, fd_set *set, int *max)
+static struct pollfd *set_fd(int fd, short events)
{
- if (fd < 0)
- return;
- FD_SET(fd, set);
- if (fd > *max)
- *max = fd;
-}
+ 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;
-static int initialize_set(fd_set *inset, fd_set *outset, int sock, int ro_sock,
- struct timeval **ptimeout)
+ 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:
+ syslog(LOG_ERR, "realloc failed, ignoring fd %d\n", fd);
+ return NULL;
+}
+
+static void initialize_fds(int sock, struct pollfd **p_sock_pollfd,
+ int ro_sock, struct pollfd **p_ro_sock_pollfd,
+ int *ptimeout)
{
- static struct timeval zero_timeout = { 0 };
struct connection *conn;
- int max = -1;
- *ptimeout = NULL;
+ memset(fds, 0, sizeof(struct pollfd) * current_array_size);
+ nr_fds = 0;
- FD_ZERO(inset);
- FD_ZERO(outset);
+ *ptimeout = -1;
if (sock != -1)
- set_fd(sock, inset, &max);
+ *p_sock_pollfd = set_fd(sock, POLLIN|POLLPRI);
if (ro_sock != -1)
- set_fd(ro_sock, inset, &max);
+ *p_ro_sock_pollfd = set_fd(ro_sock, POLLIN|POLLPRI);
if (reopen_log_pipe[0] != -1)
- set_fd(reopen_log_pipe[0], inset, &max);
+ reopen_log_pipe0_pollfd =
+ set_fd(reopen_log_pipe[0], POLLIN|POLLPRI);
if (xce_handle != NULL)
- set_fd(xc_evtchn_fd(xce_handle), inset, &max);
+ xce_pollfd = set_fd(xc_evtchn_fd(xce_handle), POLLIN|POLLPRI);
list_for_each_entry(conn, &connections, list) {
if (conn->domain) {
if (domain_can_read(conn) ||
(domain_can_write(conn) &&
!list_empty(&conn->out_list)))
- *ptimeout = &zero_timeout;
+ *ptimeout = 0;
} else {
- set_fd(conn->fd, inset, &max);
+ short events = POLLIN|POLLPRI;
if (!list_empty(&conn->out_list))
- FD_SET(conn->fd, outset);
+ events |= POLLOUT;
+ conn->pollfd = set_fd(conn->fd, events);
}
}
-
- return max;
}
/* Is child a subnode of parent, or equal? */
@@ -1770,14 +1796,13 @@ int priv_domid = 0;
int main(int argc, char *argv[])
{
- int opt, *sock, *ro_sock, max;
- fd_set inset, outset;
+ int opt, *sock, *ro_sock;
+ struct pollfd *sock_pollfd = NULL, *ro_sock_pollfd = NULL;
bool dofork = true;
bool outputpid = false;
bool no_domain_init = false;
const char *pidfile = NULL;
- int evtchn_fd = -1;
- struct timeval *timeout;
+ int timeout;
while ((opt = getopt_long(argc, argv, "DE:F:HNPS:t:T:RLVW:", options,
NULL)) != -1) {
@@ -1880,11 +1905,9 @@ int main(int argc, char *argv[])
signal(SIGHUP, trigger_reopen_log);
- if (xce_handle != NULL)
- evtchn_fd = xc_evtchn_fd(xce_handle);
-
/* Get ready to listen to the tools. */
- max = initialize_set(&inset, &outset, *sock, *ro_sock, &timeout);
+ initialize_fds(*sock, &sock_pollfd, *ro_sock, &ro_sock_pollfd,
+ &timeout);
/* Tell the kernel we're up and running. */
xenbus_notify_running();
@@ -1893,27 +1916,55 @@ int main(int argc, char *argv[])
for (;;) {
struct connection *conn, *next;
- if (select(max+1, &inset, &outset, NULL, timeout) < 0) {
+ if (poll(fds, nr_fds, timeout) < 0) {
if (errno == EINTR)
continue;
- barf_perror("Select failed");
+ barf_perror("Poll failed");
}
- if (reopen_log_pipe[0] != -1 && FD_ISSET(reopen_log_pipe[0],
&inset)) {
- char c;
- if (read(reopen_log_pipe[0], &c, 1) != 1)
- barf_perror("read failed");
- reopen_log();
+ if (reopen_log_pipe0_pollfd) {
+ if (reopen_log_pipe0_pollfd->revents & ~POLLIN) {
+ close(reopen_log_pipe[0]);
+ close(reopen_log_pipe[1]);
+ init_pipe(reopen_log_pipe);
+ } else if (reopen_log_pipe0_pollfd->revents & POLLIN) {
+ char c;
+ if (read(reopen_log_pipe[0], &c, 1) != 1)
+ barf_perror("read failed");
+ reopen_log();
+ }
+ reopen_log_pipe0_pollfd = NULL;
}
- if (*sock != -1 && FD_ISSET(*sock, &inset))
- accept_connection(*sock, true);
+ if (sock_pollfd) {
+ if (sock_pollfd->revents & ~POLLIN) {
+ barf_perror("sock poll failed");
+ break;
+ } else if (sock_pollfd->revents & POLLIN) {
+ accept_connection(*sock, true);
+ sock_pollfd = NULL;
+ }
+ }
- if (*ro_sock != -1 && FD_ISSET(*ro_sock, &inset))
- accept_connection(*ro_sock, false);
+ if (ro_sock_pollfd) {
+ if (ro_sock_pollfd->revents & ~POLLIN) {
+ barf_perror("ro sock poll failed");
+ break;
+ } else if (ro_sock_pollfd->revents & POLLIN) {
+ accept_connection(*ro_sock, false);
+ ro_sock_pollfd = NULL;
+ }
+ }
- if (evtchn_fd != -1 && FD_ISSET(evtchn_fd, &inset))
- handle_event();
+ if (xce_pollfd) {
+ if (xce_pollfd->revents & ~POLLIN) {
+ barf_perror("xce_handle poll failed");
+ break;
+ } else if (xce_pollfd->revents & POLLIN) {
+ handle_event();
+ xce_pollfd = NULL;
+ }
+ }
next = list_entry(connections.next, typeof(*conn), list);
if (&next->list != &connections)
@@ -1939,21 +1990,27 @@ int main(int argc, char *argv[])
if (talloc_free(conn) == 0)
continue;
} else {
- if (FD_ISSET(conn->fd, &inset))
+ if (conn->pollfd &&
+ !(conn->pollfd->revents &
~(POLLIN|POLLOUT)) &&
+ (conn->pollfd->revents & POLLIN))
handle_input(conn);
if (talloc_free(conn) == 0)
continue;
talloc_increase_ref_count(conn);
- if (FD_ISSET(conn->fd, &outset))
+ if (conn->pollfd &&
+ !(conn->pollfd->revents &
~(POLLIN|POLLOUT)) &&
+ (conn->pollfd->revents & POLLOUT))
handle_output(conn);
if (talloc_free(conn) == 0)
continue;
+
+ conn->pollfd = NULL;
}
}
- max = initialize_set(&inset, &outset, *sock, *ro_sock,
- &timeout);
+ initialize_fds(*sock, &sock_pollfd, *ro_sock, &ro_sock_pollfd,
+ &timeout);
}
}
diff --git a/tools/xenstore/xenstored_core.h b/tools/xenstore/xenstored_core.h
index 492ca0d..f330a87 100644
--- a/tools/xenstore/xenstored_core.h
+++ b/tools/xenstore/xenstored_core.h
@@ -60,6 +60,8 @@ struct connection
/* The file descriptor we came in on. */
int fd;
+ /* The pollfd corresponding to fd. */
+ struct pollfd *pollfd;
/* Who am I? 0 for socket connections. */
unsigned int id;
--
1.7.10.4
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