From nobody Sun Apr 21 23:47:41 2024 X-Original-To: freebsd-hackers@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id 4VN4nR5jWfz5HpQH for ; Sun, 21 Apr 2024 23:47:55 +0000 (UTC) (envelope-from asomers@gmail.com) Received: from mail-ua1-f42.google.com (mail-ua1-f42.google.com [209.85.222.42]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (2048 bits) client-digest SHA256) (Client CN "smtp.gmail.com", Issuer "GTS CA 1D4" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4VN4nR1tp6z4LyD; Sun, 21 Apr 2024 23:47:55 +0000 (UTC) (envelope-from asomers@gmail.com) Authentication-Results: mx1.freebsd.org; none Received: by mail-ua1-f42.google.com with SMTP id a1e0cc1a2514c-7e3e0b2f653so1243131241.0; Sun, 21 Apr 2024 16:47:55 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1713743273; x=1714348073; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=BgEgqqN9xzpss+9fNA45cMgyI1fMp1hGVLnbpKdZseg=; b=EAZKJap+vXnsz15e0IH0uRwbHISGTBOq6kvCMLQez7F89dWmdEBk3m85XiBvfBsnOX P/9+ekyFGcC3J4YYI1n0cvKN96kkM+tqnJ/gPxR02ryI5wyQq4lfOyEyMf+T3GNkel02 XVupjLBvT6SvONUzTkf9HOGrdddIgLHv+h1wZpIKHe1a9X6xc0qoCVHRVLjQnhxuf4tL IhkirVdlw/XWg25PQsM1q1EGaI3B4kAEOhGm6qzxtProMpX1SPeuRTd+GmtWIVm3fbCS hjuCiGjKDZcUvP+uD7OeudukEknyoxxGEoDaMD5Fn+5F/DCos/LwYRLIdGERfp/5Rqrl 4RGQ== X-Gm-Message-State: AOJu0YzWlbB8iU6C9QQMm3bHNmdv/Hfk1ctcuLAu2ZZNbGFckLctXAcX r5syoBZCvvimjDSIotGla0J9AXcQlr0hdXAXRO/t9cAPpJGkhoVww0ol67jbnBaam3aISbQPY2m pF+mgmynfMc10Slc9rXMp/F2HlfT4vQ== X-Google-Smtp-Source: AGHT+IFxDnbNtOqtZKCywqh/op1O7Fda8X/4bVveoZWZlW9OM4xBqxlVdI+6DZzDa5GDy3UQzUKLwoStLxC2vY/kBhk= X-Received: by 2002:a05:6122:2a0e:b0:4dc:d7b2:7602 with SMTP id fw14-20020a0561222a0e00b004dcd7b27602mr9166467vkb.1.1713743272966; Sun, 21 Apr 2024 16:47:52 -0700 (PDT) List-Id: Technical discussions relating to FreeBSD List-Archive: https://lists.freebsd.org/archives/freebsd-hackers List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-hackers@FreeBSD.org MIME-Version: 1.0 References: In-Reply-To: From: Alan Somers Date: Sun, 21 Apr 2024 17:47:41 -0600 Message-ID: Subject: Re: Stressing malloc(9) To: Mark Johnston Cc: FreeBSD Hackers Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Spamd-Bar: ---- X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Spamd-Result: default: False [-4.00 / 15.00]; REPLY(-4.00)[]; ASN(0.00)[asn:15169, ipnet:209.85.128.0/17, country:US] X-Rspamd-Queue-Id: 4VN4nR1tp6z4LyD On Sun, Apr 21, 2024 at 10:09=E2=80=AFAM Mark Johnston = wrote: > > On Sat, Apr 20, 2024 at 11:23:41AM -0600, Alan Somers wrote: > > On Sat, Apr 20, 2024 at 9:07=E2=80=AFAM Mark Johnston wrote: > > > > > > On Fri, Apr 19, 2024 at 04:23:51PM -0600, Alan Somers wrote: > > > > TLDR; > > > > How can I create a workload that causes malloc(9)'s performance to = plummet? > > > > > > > > Background: > > > > I recently witnessed a performance problem on a production server. > > > > Overall throughput dropped by over 30x. dtrace showed that 60% of = the > > > > CPU time was dominated by lock_delay as called by three functions: > > > > printf (via ctl_worker_thread), g_eli_alloc_data, and > > > > g_eli_write_done. One thing those three have in common is that the= y > > > > all use malloc(9). Fixing the problem was as simple as telling CTL= to > > > > stop printing so many warnings, by tuning > > > > kern.cam.ctl.time_io_secs=3D100000. > > > > > > > > But even with CTL quieted, dtrace still reports ~6% of the CPU cycl= es > > > > in lock_delay via g_eli_alloc_data. So I believe that malloc is > > > > limiting geli's performance. I would like to try replacing it with > > > > uma(9). > > > > > > What is the size of the allocations that g_eli_alloc_data() is doing? > > > malloc() is a pretty thin layer over UMA for allocations <=3D 64KB. > > > Larger allocations are handled by a different path (malloc_large()) > > > which goes directly to the kmem_* allocator functions. Those functio= ns > > > are very expensive: they're serialized by global locks and need to > > > update the pmap (and perform TLB shootdowns when memory is freed). > > > They're not meant to be used at a high rate. > > > > In my benchmarks so far, 512B. In the real application the size is > > mostly between 4k and 16k, and it's always a multiple of 4k. But it's > > sometimes great enough to use malloc_large, and it's those > > malloc_large calls that account for the majority of the time spent in > > g_eli_alloc_data. lockstat shows that malloc_large, as called by > > g_elI_alloc_data, sometimes blocks for multiple ms. > > > > But oddly, if I change the parameters so that g_eli_alloc_data > > allocates 128kB, I still don't see malloc_large getting called. And > > both dtrace and vmstat show that malloc is mostly operating on 512B > > allocations. But dtrace does confirm that g_eli_alloc_data is being > > called with 128kB arguments. Maybe something is getting inlined? > > malloc_large() is annotated __noinline, for what it's worth. > > > I > > don't understand how this is happening. I could probably figure out > > if I recompile with some extra SDT probes, though. > > What is g_eli_alloc_sz on your system? 33kiB. That's larger than I expected. When I use a larger blocksize in my benchmark, then I do indeed see malloc_large activity, and 11% of the CPU is spend in g_eli_alloc_data. I guess I'll add some UMA zones for this purpose. I'll try 256k and 512k zones, rounding up allocations as necessary. Thanks for the tip. > > > > My first guess would be that your production workload was hitting thi= s > > > path, and your benchmarks are not. If you have stack traces or lock > > > names from DTrace, that would help validate this theory, in which cas= e > > > using UMA to cache buffers would be a reasonable solution. > > > > Would that require creating an extra UMA zone for every possible geli > > allocation size above 64kB? > > Something like that. Or have a zone of maxphys-sized buffers (actually > I think it needs to be slightly larger than that?) and accept the > corresponding waste, given that these allocations are short-lived. This > is basically what g_eli_alloc_data() already does. > > > > > But on a non-production server, none of my benchmark workloads caus= es > > > > g_eli_alloc_data to break a sweat. I can't get its CPU consumption= to > > > > rise higher than 0.5%. And that's using the smallest sector size a= nd > > > > block size that I can. > > > > > > > > So my question is: does anybody have a program that can really stre= ss > > > > malloc(9)? I'd like to run it in parallel with my geli benchmarks = to > > > > see how much it interferes. > > > > > > > > -Alan > > > >