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eventpoll: support busy poll per epoll instance 

Allow busy polling on a per-epoll context basis. The per-epoll context
usec timeout value is preferred, but the pre-existing system wide sysctl
value is still supported if it specified.

busy_poll_usecs is a u32, but in a follow up patch the ioctl provided to
the user only allows setting a value from 0 to S32_MAX.

Signed-off-by: Joe Damato <jdamato@fastly.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Joe Damato 2024-02-13 06:16:42 +00:00 committed by David S. Miller
parent 723615a14b
commit 85455c795c
1 changed files with 39 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

44
fs/eventpoll.c
View File

@ -227,6 +227,8 @@ struct eventpoll {
#ifdef CONFIG_NET_RX_BUSY_POLL
/* used to track busy poll napi_id */
unsigned int napi_id;
/* busy poll timeout */
u32 busy_poll_usecs;
#endif
#ifdef CONFIG_DEBUG_LOCK_ALLOC
@ -387,11 +389,41 @@ static inline int ep_events_available(struct eventpoll *ep)
}
#ifdef CONFIG_NET_RX_BUSY_POLL
/**
* busy_loop_ep_timeout - check if busy poll has timed out. The timeout value
* from the epoll instance ep is preferred, but if it is not set fallback to
* the system-wide global via busy_loop_timeout.
*
* @start_time: The start time used to compute the remaining time until timeout.
* @ep: Pointer to the eventpoll context.
*
* Return: true if the timeout has expired, false otherwise.
*/
static bool busy_loop_ep_timeout(unsigned long start_time,
struct eventpoll *ep)
{
unsigned long bp_usec = READ_ONCE(ep->busy_poll_usecs);
if (bp_usec) {
unsigned long end_time = start_time + bp_usec;
unsigned long now = busy_loop_current_time();
return time_after(now, end_time);
} else {
return busy_loop_timeout(start_time);
}
}
static bool ep_busy_loop_on(struct eventpoll *ep)
{
return !!ep->busy_poll_usecs || net_busy_loop_on();
}
static bool ep_busy_loop_end(void *p, unsigned long start_time)
{
struct eventpoll *ep = p;
return ep_events_available(ep) || busy_loop_timeout(start_time);
return ep_events_available(ep) || busy_loop_ep_timeout(start_time, ep);
}
/*
@ -404,7 +436,7 @@ static bool ep_busy_loop(struct eventpoll *ep, int nonblock)
{
unsigned int napi_id = READ_ONCE(ep->napi_id);
if ((napi_id >= MIN_NAPI_ID) && net_busy_loop_on()) {
if (napi_id >= MIN_NAPI_ID && ep_busy_loop_on(ep)) {
napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep, false,
BUSY_POLL_BUDGET);
if (ep_events_available(ep))
@ -425,12 +457,12 @@ static bool ep_busy_loop(struct eventpoll *ep, int nonblock)
*/
static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
{
struct eventpoll *ep;
struct eventpoll *ep = epi->ep;
unsigned int napi_id;
struct socket *sock;
struct sock *sk;
if (!net_busy_loop_on())
if (!ep_busy_loop_on(ep))
return;
sock = sock_from_file(epi->ffd.file);
@ -442,7 +474,6 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
return;
napi_id = READ_ONCE(sk->sk_napi_id);
ep = epi->ep;
/* Non-NAPI IDs can be rejected
* or
@ -2058,6 +2089,9 @@ static int do_epoll_create(int flags)
error = PTR_ERR(file);
goto out_free_fd;
}
#ifdef CONFIG_NET_RX_BUSY_POLL
ep->busy_poll_usecs = 0;
#endif
ep->file = file;
fd_install(fd, file);
return fd;