From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BC9B1C2D0A3 for ; Wed, 4 Nov 2020 13:40:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 533D220867 for ; Wed, 4 Nov 2020 13:40:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="jrd/Ketx" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730087AbgKDNk1 (ORCPT ); Wed, 4 Nov 2020 08:40:27 -0500 Received: from z5.mailgun.us ([104.130.96.5]:43200 "EHLO z5.mailgun.us" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729677AbgKDNk1 (ORCPT ); Wed, 4 Nov 2020 08:40:27 -0500 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1604497226; h=Content-Transfer-Encoding: Content-Type: In-Reply-To: MIME-Version: Date: Message-ID: From: References: Cc: To: Subject: Sender; bh=RpVoMAO7pE7bPDbOQefCI2LLXeTHBoEF7ybXZpUMBOc=; b=jrd/Ketx/nfQEW/XZ0wuHoH2VcFAnqmZvxMMXkqAtl5xNeckbVwF09f76Xa/7ey0bPkwAEZs JjyArGlijg2DXRWU3XRZksTT2xBr2ooJ8lg/60i1RR16Vy1Ms8I8i3Vw6O4wgdQg17mLBYh+ M70j3dyjh/4vvLD8Smlyn3q00Yc= X-Mailgun-Sending-Ip: 104.130.96.5 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n01.prod.us-east-1.postgun.com with SMTP id 5fa2af4ac4a50c2467527410 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Wed, 04 Nov 2020 13:40:26 GMT Sender: neeraju=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 226BAC433C9; Wed, 4 Nov 2020 13:40:25 +0000 (UTC) Received: from [192.168.0.103] (unknown [124.123.167.211]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: neeraju) by smtp.codeaurora.org (Postfix) with ESMTPSA id AC7B7C433C8; Wed, 4 Nov 2020 13:40:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org AC7B7C433C8 Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=fail smtp.mailfrom=neeraju@codeaurora.org Subject: Re: [PATCH v9 4/7] rcu/trace: Add tracing for how segcb list changes To: "Joel Fernandes (Google)" , linux-kernel@vger.kernel.org Cc: Frederic Weisbecker , Josh Triplett , Lai Jiangshan , Marco Elver , Mathieu Desnoyers , "Paul E. McKenney" , rcu@vger.kernel.org, Steven Rostedt , "Uladzislau Rezki (Sony)" , fweisbec@gmail.com, neeraj.iitr10@gmail.com References: <20201103142603.1302207-1-joel@joelfernandes.org> <20201103142603.1302207-5-joel@joelfernandes.org> From: Neeraj Upadhyay Message-ID: <58c89893-1bf7-29bb-7f97-2e48755e8dd7@codeaurora.org> Date: Wed, 4 Nov 2020 19:10:17 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20201103142603.1302207-5-joel@joelfernandes.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/3/2020 7:56 PM, Joel Fernandes (Google) wrote: > Track how the segcb list changes before/after acceleration, during > queuing and during dequeuing. > > This has proved useful to discover an optimization to avoid unwanted GP > requests when there are no callbacks accelerated. The overhead is minimal as > each segment's length is now stored in the respective segment. > > Reviewed-by: Frederic Weisbecker > Reviewed-by: Neeraj Upadhyay > Signed-off-by: Joel Fernandes (Google) > --- > include/trace/events/rcu.h | 25 +++++++++++++++++++++++++ > kernel/rcu/rcu_segcblist.c | 34 ++++++++++++++++++++++++++++++++++ > kernel/rcu/rcu_segcblist.h | 5 +++++ > kernel/rcu/tree.c | 9 +++++++++ > 4 files changed, 73 insertions(+) > > diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h > index 155b5cb43cfd..5f8f2ee1a936 100644 > --- a/include/trace/events/rcu.h > +++ b/include/trace/events/rcu.h > @@ -505,6 +505,31 @@ TRACE_EVENT_RCU(rcu_callback, > __entry->qlen) > ); > > +TRACE_EVENT_RCU(rcu_segcb_stats, > + > + TP_PROTO(const char *ctx, int *cb_count, unsigned long *gp_seq), I think we need to use long[] instead of int[] for cb_count everywhere in this patch? Thanks Neeraj > + > + TP_ARGS(ctx, cb_count, gp_seq), > + > + TP_STRUCT__entry( > + __field(const char *, ctx) > + __array(int, cb_count, RCU_CBLIST_NSEGS) > + __array(unsigned long, gp_seq, RCU_CBLIST_NSEGS) > + ), > + > + TP_fast_assign( > + __entry->ctx = ctx; > + memcpy(__entry->cb_count, cb_count, RCU_CBLIST_NSEGS * sizeof(int)); > + memcpy(__entry->gp_seq, gp_seq, RCU_CBLIST_NSEGS * sizeof(unsigned long)); > + ), > + > + TP_printk("%s cb_count: (DONE=%d, WAIT=%d, NEXT_READY=%d, NEXT=%d) " > + "gp_seq: (DONE=%lu, WAIT=%lu, NEXT_READY=%lu, NEXT=%lu)", __entry->ctx, > + __entry->cb_count[0], __entry->cb_count[1], __entry->cb_count[2], __entry->cb_count[3], > + __entry->gp_seq[0], __entry->gp_seq[1], __entry->gp_seq[2], __entry->gp_seq[3]) > + > +); > + > /* > * Tracepoint for the registration of a single RCU callback of the special > * kvfree() form. The first argument is the RCU type, the second argument > diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c > index 357c19bbcb00..2a03949d0b82 100644 > --- a/kernel/rcu/rcu_segcblist.c > +++ b/kernel/rcu/rcu_segcblist.c > @@ -14,6 +14,7 @@ > #include > > #include "rcu_segcblist.h" > +#include "rcu.h" > > /* Initialize simple callback list. */ > void rcu_cblist_init(struct rcu_cblist *rclp) > @@ -328,6 +329,39 @@ void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp, > rcu_segcblist_set_seglen(rsclp, RCU_DONE_TAIL, 0); > } > > +/* > + * Return how many CBs each segment along with their gp_seq values. > + * > + * This function is O(N) where N is the number of segments. Only used from > + * tracing code which is usually disabled in production. > + */ > +#ifdef CONFIG_RCU_TRACE > +static void rcu_segcblist_countseq(struct rcu_segcblist *rsclp, > + int cbcount[RCU_CBLIST_NSEGS], > + unsigned long gpseq[RCU_CBLIST_NSEGS]) > +{ > + int i; > + > + for (i = 0; i < RCU_CBLIST_NSEGS; i++) { > + cbcount[i] = rcu_segcblist_get_seglen(rsclp, i); > + gpseq[i] = rsclp->gp_seq[i]; > + } > +} > + > +void __trace_rcu_segcb_stats(struct rcu_segcblist *rsclp, const char *context) > +{ > + int cbs[RCU_CBLIST_NSEGS]; > + unsigned long gps[RCU_CBLIST_NSEGS]; > + > + if (!trace_rcu_segcb_stats_enabled()) > + return; > + > + rcu_segcblist_countseq(rsclp, cbs, gps); > + > + trace_rcu_segcb_stats(context, cbs, gps); > +} > +#endif > + > /* > * Extract only those callbacks still pending (not yet ready to be > * invoked) from the specified rcu_segcblist structure and place them in > diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h > index cd35c9faaf51..7750734fa116 100644 > --- a/kernel/rcu/rcu_segcblist.h > +++ b/kernel/rcu/rcu_segcblist.h > @@ -103,3 +103,8 @@ void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq); > bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq); > void rcu_segcblist_merge(struct rcu_segcblist *dst_rsclp, > struct rcu_segcblist *src_rsclp); > +#ifdef CONFIG_RCU_TRACE > +void __trace_rcu_segcb_stats(struct rcu_segcblist *rsclp, const char *context); > +#else > +#define __trace_rcu_segcb_stats(...) > +#endif > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 24c00020ab83..f6c6653b3ec2 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -1497,6 +1497,8 @@ static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp) > if (!rcu_segcblist_pend_cbs(&rdp->cblist)) > return false; > > + __trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPreAcc")); > + > /* > * Callbacks are often registered with incomplete grace-period > * information. Something about the fact that getting exact > @@ -1517,6 +1519,8 @@ static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp) > else > trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccReadyCB")); > > + __trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPostAcc")); > + > return ret; > } > > @@ -2466,11 +2470,14 @@ static void rcu_do_batch(struct rcu_data *rdp) > rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl); > if (offloaded) > rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist); > + > + __trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbDequeued")); > rcu_nocb_unlock_irqrestore(rdp, flags); > > /* Invoke callbacks. */ > tick_dep_set_task(current, TICK_DEP_BIT_RCU); > rhp = rcu_cblist_dequeue(&rcl); > + > for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) { > rcu_callback_t f; > > @@ -2983,6 +2990,8 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func) > trace_rcu_callback(rcu_state.name, head, > rcu_segcblist_n_cbs(&rdp->cblist)); > > + __trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued")); > + > /* Go handle any RCU core processing required. */ > if (unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) { > __call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */ > -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation