From owner-svn-src-head@freebsd.org Wed Jun 13 19:12:31 2018 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 6230510089D3; Wed, 13 Jun 2018 19:12:31 +0000 (UTC) (envelope-from rpokala@freebsd.org) Received: from smtp.freebsd.org (smtp.freebsd.org [96.47.72.83]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "smtp.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 19C4075145; Wed, 13 Jun 2018 19:12:31 +0000 (UTC) (envelope-from rpokala@freebsd.org) Received: from [172.17.3.106] (dip-pa.panasas.com [65.205.22.243]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) (Authenticated sender: rpokala) by smtp.freebsd.org (Postfix) with ESMTPSA id D45B98085; Wed, 13 Jun 2018 19:12:30 +0000 (UTC) (envelope-from rpokala@freebsd.org) User-Agent: Microsoft-MacOutlook/10.e.0.180610 Date: Wed, 13 Jun 2018 15:12:29 -0400 Subject: Re: svn commit: r335066 - in head/sys: kern sys From: Ravi Pokala To: Warner Losh , , , Message-ID: <7D695D8A-D273-4914-9980-F4BD096A80A2@panasas.com> Thread-Topic: svn commit: r335066 - in head/sys: kern sys References: <201806131648.w5DGm7i4037714@repo.freebsd.org> In-Reply-To: <201806131648.w5DGm7i4037714@repo.freebsd.org> Mime-version: 1.0 Content-type: text/plain; charset="UTF-8" Content-transfer-encoding: 7bit X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 13 Jun 2018 19:12:31 -0000 Hi Warner, I have many questions... "Car limit"? I'm not sure what you mean by that? This change starts tracking the total number of BIOs on the queue, but doesn't actually do anything with that value. When there are more requests batched than the limit, your comment say you "start over", and the code says you bioq_insert_tail(). Why does the latter imply "start(ing) over"? Thanks, Ravi (rpokala@) -----Original Message----- From: on behalf of Warner Losh Date: 2018-06-13, Wednesday at 12:48 To: , , Subject: svn commit: r335066 - in head/sys: kern sys Author: imp Date: Wed Jun 13 16:48:07 2018 New Revision: 335066 URL: https://svnweb.freebsd.org/changeset/base/335066 Log: Implement a 'car limit' for bioq. Allow one to implement a 'car limit' for bioq_disksort. debug.bioq_batchsize sets the size of car limit. Every time we queue that many requests, we start over so that we limit the latency for requests when the software queue depths are large. A value of '0', the default, means to revert to the old behavior. Sponsored by: Netflix Modified: head/sys/kern/subr_disk.c head/sys/sys/bio.h Modified: head/sys/kern/subr_disk.c ============================================================================== --- head/sys/kern/subr_disk.c Wed Jun 13 15:58:33 2018 (r335065) +++ head/sys/kern/subr_disk.c Wed Jun 13 16:48:07 2018 (r335066) @@ -23,8 +23,13 @@ __FBSDID("$FreeBSD$"); #include #include #include +#include #include +static int bioq_batchsize = 0; +SYSCTL_INT(_debug, OID_AUTO, bioq_batchsize, CTLFLAG_RW, + &bioq_batchsize, 0, "BIOQ batch size"); + /*- * Disk error is the preface to plaintive error messages * about failing disk transfers. It prints messages of the form @@ -152,6 +157,8 @@ bioq_init(struct bio_queue_head *head) TAILQ_INIT(&head->queue); head->last_offset = 0; head->insert_point = NULL; + head->total = 0; + head->batched = 0; } void @@ -165,6 +172,7 @@ bioq_remove(struct bio_queue_head *head, struct bio *b head->insert_point = NULL; TAILQ_REMOVE(&head->queue, bp, bio_queue); + head->total--; } void @@ -183,6 +191,8 @@ bioq_insert_head(struct bio_queue_head *head, struct b if (head->insert_point == NULL) head->last_offset = bp->bio_offset; TAILQ_INSERT_HEAD(&head->queue, bp, bio_queue); + head->total++; + head->batched = 0; } void @@ -190,6 +200,7 @@ bioq_insert_tail(struct bio_queue_head *head, struct b { TAILQ_INSERT_TAIL(&head->queue, bp, bio_queue); + head->total++; head->insert_point = bp; head->last_offset = bp->bio_offset; } @@ -248,6 +259,11 @@ bioq_disksort(struct bio_queue_head *head, struct bio return; } + if (bioq_batchsize > 0 && head->batched > bioq_batchsize) { + bioq_insert_tail(head, bp); + return; + } + prev = NULL; key = bioq_bio_key(head, bp); cur = TAILQ_FIRST(&head->queue); @@ -266,4 +282,6 @@ bioq_disksort(struct bio_queue_head *head, struct bio TAILQ_INSERT_HEAD(&head->queue, bp, bio_queue); else TAILQ_INSERT_AFTER(&head->queue, prev, bp, bio_queue); + head->total++; + head->batched++; } Modified: head/sys/sys/bio.h ============================================================================== --- head/sys/sys/bio.h Wed Jun 13 15:58:33 2018 (r335065) +++ head/sys/sys/bio.h Wed Jun 13 16:48:07 2018 (r335066) @@ -138,6 +138,8 @@ struct bio_queue_head { TAILQ_HEAD(bio_queue, bio) queue; off_t last_offset; struct bio *insert_point; + int total; + int batched; }; extern struct vm_map *bio_transient_map;