From 2d48d67fa8cd129ea85ea02d91b4a793286866f8 Mon Sep 17 00:00:00 2001 From: Eliezer Tamir Date: Mon, 24 Jun 2013 10:28:03 +0300 Subject: [PATCH] net: poll/select low latency socket support 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 Signed-off-by: David S. Miller --- Documentation/sysctl/net.txt | 18 +++++++++++++++-- fs/select.c | 34 +++++++++++++++++++++++++++----- include/net/ll_poll.h | 35 +++++++++++++++++++++------------ include/uapi/asm-generic/poll.h | 2 ++ net/core/sock.c | 2 +- net/core/sysctl_net_core.c | 8 ++++++++ net/socket.c | 14 ++++++++++++- 7 files changed, 91 insertions(+), 22 deletions(-) diff --git a/Documentation/sysctl/net.txt b/Documentation/sysctl/net.txt index 5369879eafe2..e658bbfb641f 100644 --- a/Documentation/sysctl/net.txt +++ b/Documentation/sysctl/net.txt @@ -50,13 +50,27 @@ The maximum number of packets that kernel can handle on a NAPI interrupt, it's a Per-CPU variable. Default: 64 -low_latency_poll +low_latency_read ---------------- -Low latency busy poll timeout. (needs CONFIG_NET_LL_RX_POLL) +Low latency busy poll timeout for socket reads. (needs CONFIG_NET_LL_RX_POLL) Approximate time in us to spin waiting for packets on the device queue. +This sets the default value of the SO_LL socket option. +Can be set or overridden per socket by setting socket option SO_LL. Recommended value is 50. May increase power usage. Default: 0 (off) +low_latency_poll +---------------- +Low latency busy poll timeout for poll and select. (needs CONFIG_NET_LL_RX_POLL) +Approximate time in us to spin waiting for packets on the device queue. +Recommended value depends on the number of sockets you poll on. +For several sockets 50, for several hundreds 100. +For more than that you probably want to use epoll. +Note that only sockets with SO_LL set will be busy polled, so you want to either +selectively set SO_LL on those sockets or set sysctl.net.low_latency_read globally. +May increase power usage. +Default: 0 (off) + rmem_default ------------ diff --git a/fs/select.c b/fs/select.c index 8c1c96c27062..79b876eb91da 100644 --- a/fs/select.c +++ b/fs/select.c @@ -27,6 +27,7 @@ #include #include #include +#include #include @@ -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 diff --git a/include/net/ll_poll.h b/include/net/ll_poll.h index fcc7c365cee5..5bf2b3a6129e 100644 --- a/include/net/ll_poll.h +++ b/include/net/ll_poll.h @@ -30,6 +30,7 @@ #ifdef CONFIG_NET_LL_RX_POLL struct napi_struct; +extern unsigned int sysctl_net_ll_read __read_mostly; extern unsigned int sysctl_net_ll_poll __read_mostly; /* return values from ndo_ll_poll */ @@ -38,17 +39,18 @@ extern unsigned int sysctl_net_ll_poll __read_mostly; /* we can use sched_clock() because we don't care much about precision * we only care that the average is bounded + * we don't mind a ~2.5% imprecision so <<10 instead of *1000 + * sk->sk_ll_usec is a u_int so this can't overflow */ -static inline u64 ll_end_time(struct sock *sk) +static inline u64 ll_sk_end_time(struct sock *sk) { - u64 end_time = ACCESS_ONCE(sk->sk_ll_usec); - - /* we don't mind a ~2.5% imprecision - * sk->sk_ll_usec is a u_int so this can't overflow - */ - end_time = (end_time << 10) + sched_clock(); + return ((u64)ACCESS_ONCE(sk->sk_ll_usec) << 10) + sched_clock(); +} - return end_time; +/* in poll/select we use the global sysctl_net_ll_poll value */ +static inline u64 ll_end_time(void) +{ + return ((u64)ACCESS_ONCE(sysctl_net_ll_poll) << 10) + sched_clock(); } static inline bool sk_valid_ll(struct sock *sk) @@ -62,10 +64,13 @@ static inline bool can_poll_ll(u64 end_time) return !time_after64(sched_clock(), end_time); } +/* when used in sock_poll() nonblock is known at compile time to be true + * so the loop and end_time will be optimized out + */ static inline bool sk_poll_ll(struct sock *sk, int nonblock) { + u64 end_time = nonblock ? 0 : ll_sk_end_time(sk); const struct net_device_ops *ops; - u64 end_time = ll_end_time(sk); struct napi_struct *napi; int rc = false; @@ -84,7 +89,6 @@ static inline bool sk_poll_ll(struct sock *sk, int nonblock) goto out; do { - rc = ops->ndo_ll_poll(napi); if (rc == LL_FLUSH_FAILED) @@ -95,8 +99,8 @@ static inline bool sk_poll_ll(struct sock *sk, int nonblock) NET_ADD_STATS_BH(sock_net(sk), LINUX_MIB_LOWLATENCYRXPACKETS, rc); - } while (skb_queue_empty(&sk->sk_receive_queue) - && can_poll_ll(end_time) && !nonblock); + } while (!nonblock && skb_queue_empty(&sk->sk_receive_queue) && + can_poll_ll(end_time)); rc = !skb_queue_empty(&sk->sk_receive_queue); out: @@ -118,7 +122,12 @@ static inline void sk_mark_ll(struct sock *sk, struct sk_buff *skb) #else /* CONFIG_NET_LL_RX_POLL */ -static inline u64 ll_end_time(struct sock *sk) +static inline u64 sk_ll_end_time(struct sock *sk) +{ + return 0; +} + +static inline u64 ll_end_time(void) { return 0; } diff --git a/include/uapi/asm-generic/poll.h b/include/uapi/asm-generic/poll.h index 9ce7f44aebd2..4aee586979ca 100644 --- a/include/uapi/asm-generic/poll.h +++ b/include/uapi/asm-generic/poll.h @@ -30,6 +30,8 @@ #define POLLFREE 0x4000 /* currently only for epoll */ +#define POLL_LL 0x8000 + struct pollfd { int fd; short events; diff --git a/net/core/sock.c b/net/core/sock.c index 1e744b12fda3..b6c619f4d47b 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -2307,7 +2307,7 @@ void sock_init_data(struct socket *sock, struct sock *sk) #ifdef CONFIG_NET_LL_RX_POLL sk->sk_napi_id = 0; - sk->sk_ll_usec = sysctl_net_ll_poll; + sk->sk_ll_usec = sysctl_net_ll_read; #endif /* diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c index 62702c2053de..afc677eadd93 100644 --- a/net/core/sysctl_net_core.c +++ b/net/core/sysctl_net_core.c @@ -306,6 +306,14 @@ static struct ctl_table net_core_table[] = { .mode = 0644, .proc_handler = proc_dointvec }, + { + .procname = "low_latency_read", + .data = &sysctl_net_ll_read, + .maxlen = sizeof(unsigned int), + .mode = 0644, + .proc_handler = proc_dointvec + }, +# #endif #endif /* CONFIG_NET */ { diff --git a/net/socket.c b/net/socket.c index 3eec3f76b49c..4da14cbd49b6 100644 --- a/net/socket.c +++ b/net/socket.c @@ -107,6 +107,7 @@ #include #ifdef CONFIG_NET_LL_RX_POLL +unsigned int sysctl_net_ll_read __read_mostly; unsigned int sysctl_net_ll_poll __read_mostly; #endif @@ -1147,13 +1148,24 @@ EXPORT_SYMBOL(sock_create_lite); /* No kernel lock held - perfect */ static unsigned int sock_poll(struct file *file, poll_table *wait) { + unsigned int ll_flag = 0; struct socket *sock; /* * We can't return errors to poll, so it's either yes or no. */ sock = file->private_data; - return sock->ops->poll(file, sock, wait); + + if (sk_valid_ll(sock->sk)) { + /* this socket can poll_ll so tell the system call */ + ll_flag = POLL_LL; + + /* once, only if requested by syscall */ + if (wait && (wait->_key & POLL_LL)) + sk_poll_ll(sock->sk, 1); + } + + return ll_flag | sock->ops->poll(file, sock, wait); } static int sock_mmap(struct file *file, struct vm_area_struct *vma) -- 2.20.1