From patchwork Tue Jul 2 08:38:55 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eliezer Tamir X-Patchwork-Id: 256299 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 63CB32C009C for ; Tue, 2 Jul 2013 18:39:35 +1000 (EST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932360Ab3GBIjH (ORCPT ); Tue, 2 Jul 2013 04:39:07 -0400 Received: from mga09.intel.com ([134.134.136.24]:15002 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753236Ab3GBIjB (ORCPT ); Tue, 2 Jul 2013 04:39:01 -0400 Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga102.jf.intel.com with ESMTP; 02 Jul 2013 01:36:36 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.87,980,1363158000"; d="scan'208";a="339171987" Received: from etamir-mobl.ger.corp.intel.com (HELO [10.12.67.67]) ([10.12.67.67]) by orsmga001.jf.intel.com with ESMTP; 02 Jul 2013 01:38:56 -0700 Message-ID: <51D2919F.7050007@linux.intel.com> Date: Tue, 02 Jul 2013 11:38:55 +0300 From: Eliezer Tamir User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130620 Thunderbird/17.0.7 MIME-Version: 1.0 To: David Miller CC: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, willemb@google.com, erdnetdev@gmail.com, andi@firstfloor.org, hpa@zytor.com, devel-lists@codyps.com, eliezer@tamir.org.il Subject: Re: [PATCH net-next 0/2] net: lls cleanup patches References: <20130628125918.14419.36214.stgit@ladj378.jer.intel.com> <20130701.140833.1705666564717621661.davem@davemloft.net> In-Reply-To: <20130701.140833.1705666564717621661.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 02/07/2013 00:08, David Miller wrote: > From: Eliezer Tamir > Date: Fri, 28 Jun 2013 15:59:18 +0300 > >> Here are two cleanup patches. >> >> 1. fix warning from debug_smp_processor_id(). >> - reported by Cody P Schafer. >> > Applied, but like Ben said perhaps you want to remember the last cpu you > got the sched_clock() measurement from and abort the ll poll if it changes > on you instead of using a comparison between two cpus. > > But then again, since preemption is enabled, the cpu could change > back and forth during the sched_clock() call, so you wouldn't be able > to reliably detect this anyways. > > In the grand scheme of things all of this probably doesn't matter at > all. The only thing that really worries me, is the possibility of time on the new cpu to be completely random, then we could be back in the range where time_after() will be false again and end up polling for another year. A simple way to limit the damage would be to use time_in_range() instead of time_after(), then if we have a completely random time we would be out of the range and fail safely. would something like this be an acceptable solution? --- [PATCH net-next] net: convert lls to use time_in_range() Time in range will fail safely if we move to a different cpu with an extremely large clock skew. Add time_in_range64() and convert lls to use it. Signed-of-by: Eliezer Tamir --- fs/select.c | 10 ++++++---- include/linux/jiffies.h | 4 ++++ include/net/ll_poll.h | 24 +++++++++++++++--------- 3 files changed, 25 insertions(+), 13 deletions(-) out: -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/fs/select.c b/fs/select.c index 3654075..f28a585 100644 --- a/fs/select.c +++ b/fs/select.c @@ -403,7 +403,8 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time) int retval, i, timed_out = 0; unsigned long slack = 0; unsigned int ll_flag = ll_get_flag(); - u64 ll_time = ll_end_time(); + u64 ll_start = ll_start_time(ll_flag); + u64 ll_time = ll_run_time(); rcu_read_lock(); retval = max_select_fd(n, fds); @@ -498,7 +499,7 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time) } /* only if on, have sockets with POLL_LL and not out of time */ - if (ll_flag && can_ll && can_poll_ll(ll_time)) + if (ll_flag && can_ll && can_poll_ll(ll_start, ll_time)) continue; /* @@ -770,7 +771,8 @@ static int do_poll(unsigned int nfds, struct poll_list *list, int timed_out = 0, count = 0; unsigned long slack = 0; unsigned int ll_flag = ll_get_flag(); - u64 ll_time = ll_end_time(); + u64 ll_start = ll_start_time(ll_flag); + u64 ll_time = ll_run_time(); /* Optimise the no-wait case */ if (end_time && !end_time->tv_sec && !end_time->tv_nsec) { @@ -819,7 +821,7 @@ static int do_poll(unsigned int nfds, struct poll_list *list, break; /* only if on, have sockets with POLL_LL and not out of time */ - if (ll_flag && can_ll && can_poll_ll(ll_time)) + if (ll_flag && can_ll && can_poll_ll(ll_start, ll_time)) continue; /* diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h index 8fb8edf..37b7354 100644 --- a/include/linux/jiffies.h +++ b/include/linux/jiffies.h @@ -139,6 +139,10 @@ static inline u64 get_jiffies_64(void) ((__s64)(a) - (__s64)(b) >= 0)) #define time_before_eq64(a,b) time_after_eq64(b,a) +#define time_in_range64(a,b,c) \ + (time_after_eq64(a,b) && \ + time_before_eq64(a,c)) + /* * These four macros compare jiffies and 'a' for convenience. */ diff --git a/include/net/ll_poll.h b/include/net/ll_poll.h index 6c06f7c..61c2daf 100644 --- a/include/net/ll_poll.h +++ b/include/net/ll_poll.h @@ -67,19 +67,23 @@ static inline u64 ll_sched_clock(void) /* 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_sk_end_time(struct sock *sk) +static inline u64 ll_sk_run_time(struct sock *sk) { - return ((u64)ACCESS_ONCE(sk->sk_ll_usec) << 10) + ll_sched_clock(); + return (u64)ACCESS_ONCE(sk->sk_ll_usec) << 10; } /* in poll/select we use the global sysctl_net_ll_poll value * only call sched_clock() if enabled */ -static inline u64 ll_end_time(void) +static inline u64 ll_run_time(void) { - u64 end_time = ACCESS_ONCE(sysctl_net_ll_poll); + return (u64)ACCESS_ONCE(sysctl_net_ll_poll) << 10; +} - return end_time ? (end_time << 10) + ll_sched_clock() : 0; +/* if flag is not set we don't need to know the time */ +static inline u64 ll_start_time(unsigned int flag) +{ + return flag ? ll_sched_clock() : 0; } static inline bool sk_valid_ll(struct sock *sk) @@ -88,9 +92,10 @@ static inline bool sk_valid_ll(struct sock *sk) !need_resched() && !signal_pending(current); } -static inline bool can_poll_ll(u64 end_time) +static inline bool can_poll_ll(u64 start_time, u64 run_time) { - return !time_after64(ll_sched_clock(), end_time); + return time_in_range64(ll_sched_clock(), start_time, + start_time + run_time); } /* when used in sock_poll() nonblock is known at compile time to be true @@ -98,7 +103,8 @@ static inline bool can_poll_ll(u64 end_time) */ static inline bool sk_poll_ll(struct sock *sk, int nonblock) { - u64 end_time = nonblock ? 0 : ll_sk_end_time(sk); + u64 start_time = ll_start_time(!nonblock); + u64 run_time = ll_sk_run_time(sk); const struct net_device_ops *ops; struct napi_struct *napi; int rc = false; @@ -129,7 +135,7 @@ static inline bool sk_poll_ll(struct sock *sk, int nonblock) LINUX_MIB_LOWLATENCYRXPACKETS, rc); } while (!nonblock && skb_queue_empty(&sk->sk_receive_queue) && - can_poll_ll(end_time)); + can_poll_ll(start_time, run_time)); rc = !skb_queue_empty(&sk->sk_receive_queue);