From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Whitehead Subject: [PATCH net-next] Replace 2 jiffies with sysctl netdev_budget_usecs to enable softirq tuning Date: Wed, 19 Apr 2017 12:37:10 -0400 Message-ID: <1492619830-7561-1-git-send-email-tedheadster@gmail.com> Cc: Matthew Whitehead To: netdev@vger.kernel.org Return-path: Received: from mail-qt0-f194.google.com ([209.85.216.194]:35774 "EHLO mail-qt0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S938166AbdDSQhS (ORCPT ); Wed, 19 Apr 2017 12:37:18 -0400 Received: by mail-qt0-f194.google.com with SMTP id o36so3904135qtb.2 for ; Wed, 19 Apr 2017 09:37:17 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: Constants used for tuning are generally a bad idea, especially as hardware changes over time. Replace the constant 2 jiffies with sysctl variable netdev_budget_usecs to enable sysadmins to tune the softirq processing. Also document the variable. For example, a very fast machine might tune this to 1000 microseconds, while my regression testing 486DX-25 needs it to be 4000 microseconds on a nearly idle network to prevent time_squeeze from being incremented. Version 2: changed jiffies to microseconds for predictable units. Signed-off-by: Matthew Whitehead --- Documentation/sysctl/net.txt | 11 ++++++++++- include/linux/netdevice.h | 1 + include/uapi/linux/sysctl.h | 1 + kernel/sysctl_binary.c | 1 + net/core/dev.c | 4 +++- net/core/sysctl_net_core.c | 8 ++++++++ 6 files changed, 24 insertions(+), 2 deletions(-) diff --git a/Documentation/sysctl/net.txt b/Documentation/sysctl/net.txt index 2ebabc9..14db18c 100644 --- a/Documentation/sysctl/net.txt +++ b/Documentation/sysctl/net.txt @@ -188,7 +188,16 @@ netdev_budget Maximum number of packets taken from all interfaces in one polling cycle (NAPI poll). In one polling cycle interfaces which are registered to polling are -probed in a round-robin manner. +probed in a round-robin manner. Also, a polling cycle may not exceed +netdev_budget_usecs microseconds, even if netdev_budget has not been +exhausted. + +netdev_budget_usecs +--------------------- + +Maximum number of microseconds in one NAPI polling cycle. Polling +will exit when either netdev_budget_usecs have elapsed during the +poll cycle or the number of packets processed reaches netdev_budget. netdev_max_backlog ------------------ diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index 97456b25..2fc72a5 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -3305,6 +3305,7 @@ static __always_inline int ____dev_forward_skb(struct net_device *dev, void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev); extern int netdev_budget; +extern unsigned int netdev_budget_usecs; /* Called by rtnetlink.c:rtnl_unlock() */ void netdev_run_todo(void); diff --git a/include/uapi/linux/sysctl.h b/include/uapi/linux/sysctl.h index d2b1215..a1f1f25 100644 --- a/include/uapi/linux/sysctl.h +++ b/include/uapi/linux/sysctl.h @@ -274,6 +274,7 @@ enum NET_CORE_AEVENT_ETIME=20, NET_CORE_AEVENT_RSEQTH=21, NET_CORE_WARNINGS=22, + NET_CORE_BUDGET_USECS=23, }; /* /proc/sys/net/ethernet */ diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c index ece4b17..4ee3e49 100644 --- a/kernel/sysctl_binary.c +++ b/kernel/sysctl_binary.c @@ -197,6 +197,7 @@ struct bin_table { { CTL_INT, NET_CORE_AEVENT_ETIME, "xfrm_aevent_etime" }, { CTL_INT, NET_CORE_AEVENT_RSEQTH, "xfrm_aevent_rseqth" }, { CTL_INT, NET_CORE_WARNINGS, "warnings" }, + { CTL_INT, NET_CORE_BUDGET_USECS, "netdev_budget_usecs" }, {}, }; diff --git a/net/core/dev.c b/net/core/dev.c index 533a6d6..78627e5 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -3441,6 +3441,7 @@ int dev_queue_xmit_accel(struct sk_buff *skb, void *accel_priv) int netdev_tstamp_prequeue __read_mostly = 1; int netdev_budget __read_mostly = 300; +unsigned int __read_mostly netdev_budget_usecs = 2000; int weight_p __read_mostly = 64; /* old backlog weight */ int dev_weight_rx_bias __read_mostly = 1; /* bias for backlog weight */ int dev_weight_tx_bias __read_mostly = 1; /* bias for output_queue quota */ @@ -5310,7 +5311,8 @@ static int napi_poll(struct napi_struct *n, struct list_head *repoll) static __latent_entropy void net_rx_action(struct softirq_action *h) { struct softnet_data *sd = this_cpu_ptr(&softnet_data); - unsigned long time_limit = jiffies + 2; + unsigned long time_limit = jiffies + + usecs_to_jiffies(netdev_budget_usecs); int budget = netdev_budget; LIST_HEAD(list); LIST_HEAD(repoll); diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c index 7f9cc40..ea23254 100644 --- a/net/core/sysctl_net_core.c +++ b/net/core/sysctl_net_core.c @@ -452,6 +452,14 @@ static int proc_do_rss_key(struct ctl_table *table, int write, .extra1 = &one, .extra2 = &max_skb_frags, }, + { + .procname = "netdev_budget_usecs", + .data = &netdev_budget_usecs, + .maxlen = sizeof(unsigned int), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = &zero, + }, { } }; -- 1.8.3.1