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net: poll/select low latency socket support

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select/poll busy-poll support.

Split sysctl value into two separate ones, one for read and one for poll.
updated Documentation/sysctl/net.txt

Add a new poll flag POLL_LL. When this flag is set, sock_poll will call
sk_poll_ll if possible. sock_poll sets this flag in its return value
to indicate to select/poll when a socket that can busy poll is found.

When poll/select have nothing to report, call the low-level
sock_poll again until we are out of time or we find something.

Once the system call finds something, it stops setting POLL_LL, so it can
return the result to the user ASAP.

Signed-off-by: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eliezer Tamir 2013-06-24 10:28:03 +03:00 • committed by David S. Miller
parent e4f2379db6
commit 2d48d67fa8
7 changed files with 91 additions and 22 deletions
Download patch file Download diff file Expand all files Collapse all files

34
fs/select.c
View file

@ -27,6 +27,7 @@
#include <linux/rcupdate.h>
#include <linux/hrtimer.h>
#include <linux/sched/rt.h>
#include <net/ll_poll.h>
#include <asm/uaccess.h>
@ -384,9 +385,10 @@ get_max:
#define POLLEX_SET (POLLPRI)
static inline void wait_key_set(poll_table *wait, unsigned long in,
unsigned long out, unsigned long bit)
unsigned long out, unsigned long bit,
unsigned int ll_flag)
{
wait->_key = POLLEX_SET;
wait->_key = POLLEX_SET | ll_flag;
if (in & bit)
wait->_key |= POLLIN_SET;
if (out & bit)
@ -400,6 +402,8 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
poll_table *wait;
int retval, i, timed_out = 0;
unsigned long slack = 0;
unsigned int ll_flag = POLL_LL;
u64 ll_time = ll_end_time();
rcu_read_lock();
retval = max_select_fd(n, fds);
@ -422,6 +426,7 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
retval = 0;
for (;;) {
unsigned long *rinp, *routp, *rexp, *inp, *outp, *exp;
bool can_ll = false;
inp = fds->in; outp = fds->out; exp = fds->ex;
rinp = fds->res_in; routp = fds->res_out; rexp = fds->res_ex;
@ -449,7 +454,8 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
f_op = f.file->f_op;
mask = DEFAULT_POLLMASK;
if (f_op && f_op->poll) {
wait_key_set(wait, in, out, bit);
wait_key_set(wait, in, out,
bit, ll_flag);
mask = (*f_op->poll)(f.file, wait);
}
fdput(f);
@ -468,6 +474,11 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
retval++;
wait->_qproc = NULL;
}
if (mask & POLL_LL)
can_ll = true;
/* got something, stop busy polling */
if (retval)
ll_flag = 0;
}
}
if (res_in)
@ -486,6 +497,9 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
break;
}
if (can_ll && can_poll_ll(ll_time))
continue;
/*
* If this is the first loop and we have a timeout
* given, then we convert to ktime_t and set the to
@ -717,7 +731,8 @@ struct poll_list {
* pwait poll_table will be used by the fd-provided poll handler for waiting,
* if pwait->_qproc is non-NULL.
*/
static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait)
static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait,
bool *can_ll, unsigned int ll_flag)
{
unsigned int mask;
int fd;
@ -731,7 +746,10 @@ static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait)
mask = DEFAULT_POLLMASK;
if (f.file->f_op && f.file->f_op->poll) {
pwait->_key = pollfd->events|POLLERR|POLLHUP;
pwait->_key |= ll_flag;
mask = f.file->f_op->poll(f.file, pwait);
if (mask & POLL_LL)
*can_ll = true;
}
/* Mask out unneeded events. */
mask &= pollfd->events | POLLERR | POLLHUP;
@ -750,6 +768,8 @@ static int do_poll(unsigned int nfds, struct poll_list *list,
ktime_t expire, *to = NULL;
int timed_out = 0, count = 0;
unsigned long slack = 0;
unsigned int ll_flag = POLL_LL;
u64 ll_time = ll_end_time();
/* Optimise the no-wait case */
if (end_time && !end_time->tv_sec && !end_time->tv_nsec) {
@ -762,6 +782,7 @@ static int do_poll(unsigned int nfds, struct poll_list *list,
for (;;) {
struct poll_list *walk;
bool can_ll = false;
for (walk = list; walk != NULL; walk = walk->next) {
struct pollfd * pfd, * pfd_end;
@ -776,9 +797,10 @@ static int do_poll(unsigned int nfds, struct poll_list *list,
* this. They'll get immediately deregistered
* when we break out and return.
*/
if (do_pollfd(pfd, pt)) {
if (do_pollfd(pfd, pt, &can_ll, ll_flag)) {
count++;
pt->_qproc = NULL;
ll_flag = 0;
}
}
}
@ -795,6 +817,8 @@ static int do_poll(unsigned int nfds, struct poll_list *list,
if (count || timed_out)
break;
if (can_ll && can_poll_ll(ll_time))
continue;
/*
* If this is the first loop and we have a timeout
* given, then we convert to ktime_t and set the to