From owner-freebsd-arch@freebsd.org Fri Nov 13 19:09:48 2020 Return-Path: Delivered-To: freebsd-arch@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 122D52EB28C for ; Fri, 13 Nov 2020 19:09:48 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 4CXp1l1J96z4mCB for ; Fri, 13 Nov 2020 19:09:46 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.16.1/8.16.1) with ESMTPS id 0ADJ9bHs025664 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Fri, 13 Nov 2020 21:09:40 +0200 (EET) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua 0ADJ9bHs025664 Received: (from kostik@localhost) by tom.home (8.16.1/8.16.1/Submit) id 0ADJ9bhc025663; Fri, 13 Nov 2020 21:09:37 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Fri, 13 Nov 2020 21:09:37 +0200 From: Konstantin Belousov To: Warner Losh Cc: "freebsd-arch@freebsd.org" Subject: Re: MAXPHYS bump for FreeBSD 13 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spam-Status: No, score=-1.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FORGED_GMAIL_RCVD,FREEMAIL_FROM, NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on tom.home X-Rspamd-Queue-Id: 4CXp1l1J96z4mCB X-Spamd-Bar: - Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=fail reason="No valid SPF, No valid DKIM" header.from=gmail.com (policy=none); spf=softfail (mx1.freebsd.org: 2001:470:d5e7:1::1 is neither permitted nor denied by domain of kostikbel@gmail.com) smtp.mailfrom=kostikbel@gmail.com X-Spamd-Result: default: False [-1.00 / 15.00]; ARC_NA(0.00)[]; TO_DN_EQ_ADDR_SOME(0.00)[]; DMARC_POLICY_SOFTFAIL(0.10)[gmail.com : No valid SPF, No valid DKIM,none]; RCVD_TLS_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FREEMAIL_FROM(0.00)[gmail.com]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.10)[text/plain]; HAS_XAW(0.00)[]; RBL_DBL_DONT_QUERY_IPS(0.00)[2001:470:d5e7:1::1:from]; R_SPF_SOFTFAIL(0.00)[~all:c]; NEURAL_SPAM_SHORT(1.00)[0.999]; SPAMHAUS_ZRD(0.00)[2001:470:d5e7:1::1:from:127.0.2.255]; TO_MATCH_ENVRCPT_SOME(0.00)[]; RCPT_COUNT_TWO(0.00)[2]; NEURAL_HAM_MEDIUM(-1.00)[-1.000]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; FREEMAIL_ENVFROM(0.00)[gmail.com]; ASN(0.00)[asn:6939, ipnet:2001:470::/32, country:US]; MIME_TRACE(0.00)[0:+]; MAILMAN_DEST(0.00)[freebsd-arch]; RCVD_COUNT_TWO(0.00)[2] X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 13 Nov 2020 19:09:48 -0000 On Fri, Nov 13, 2020 at 11:33:30AM -0700, Warner Losh wrote: > Greetings, > > We currently have a MAXPHYS of 128k. This is the maximum size of I/Os that > we normally use (though there are exceptions). > > I'd like to propose that we bump MAXPHYS to 1MB, as well as bumping > DFLTPHYS to 1MB. > > 128k was good back in the 90s/2000s when memory was smaller, drives did > smaller I/Os, etc. Now, however, it doesn't make much sense. Modern I/O > devices can easily do 1MB or more and there's performance benefits from > scheduling larger I/Os. > > Bumping this will mean larger struct buf and struct bio. Without some > concerted effort, it's hard to make this be a sysctl tunable. While that's > desirable, perhaps, it shouldn't gate this bump. The increase in size for > 1MB is modest enough. To put the specific numbers, for struct buf it means increase by 1792 bytes. For bio it does not, because it does not embed vm_page_t[] into the structure. Worse, typical struct buf addend for excess vm_page pointers is going to be unused, because normal size of the UFS block is 32K. It is going to be only used by clusters and physbufs. So I object against bumping this value without reworking buffers handling of b_pages[]. Most straightforward approach is stop using MAXPHYS to size this array, and use external array for clusters. Pbufs can embed large array. > > The NVMe driver currently is limited to 1MB transfers due to limitations in > the NVMe scatter gather lists and a desire to preallocate as much as > possible up front. Most NVMe drivers have maximum transfer sizes between > 128k and 1MB, with larger being the trend. > > The mp[rs] drivers can use larger MAXPHYS, though resource limitations on > some cards hamper bumping it beyond about 2MB. > > The AHCI driver is happy with 1MB and larger sizes. > > Netflix has run MAXPHYS of 8MB for years, though that's likely 2x too large > even for our needs due to limiting factors in the upper layers making it > hard to schedule I/Os larger than 3-4MB reliably. > > So this should be a relatively low risk, and high benefit. > > I don't think other kernel tunables need to change, but I always run into > trouble with runningbufs :) > > Comments? Anything I forgot? > > Warner > _______________________________________________ > freebsd-arch@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-arch > To unsubscribe, send any mail to "freebsd-arch-unsubscribe@freebsd.org"