From nobody Fri Nov 14 06:41:30 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=pass(p=quarantine dis=none) header.from=crudebyte.com ARC-Seal: i=1; a=rsa-sha256; t=1585261757; cv=none; d=zohomail.com; s=zohoarc; b=YqF1fZKq2aWYefSVCxR5mshn9/38El+G6VJZfvsHb4f5+KCp6JkN5Yp95wHtJTZINavpcIXLKmjKhjw425FHJ0mzS1wQsktmuV4UiWU8i2pLgwZw6YupU5plMRoCXH5IwcL3EMSbUvU9RKBEm9CSMH8rN6C77YpToJfFSLS0pkE= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1585261757; h=Cc:Date:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:Message-ID:References:Sender:Subject:To; bh=jPdUMVvPDb49VGrJsLB5Dy+OTfiFUvEBcazVO3auyKA=; b=UURyEX8zO/5GdpL7Tka4i5oeu4T1f5XhPrD13X1G6tmCee7RfDgG9Y7WQKrQuUjvWHZEJiMfi0HaX6Jo/SWl/7fSCdghU3KdOak4VjsnWZXW1hqz39oMEmNJh+ZymwXH+Bf4NFyiM1QFYiH/UhtKG9MjwQNxSm2gCoAzKOpfulA= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=pass header.from= (p=quarantine dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1585261756965664.20801676491; Thu, 26 Mar 2020 15:29:16 -0700 (PDT) Received: from localhost ([::1]:33538 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jHazz-0004vU-O5 for importer@patchew.org; Thu, 26 Mar 2020 18:29:15 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:51914) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from <7c4e49a783c7b2f77aa81794892cf08b4feba914@lizzy.crudebyte.com>) id 1jHaz5-0004HY-47 for qemu-devel@nongnu.org; Thu, 26 Mar 2020 18:28:20 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from <7c4e49a783c7b2f77aa81794892cf08b4feba914@lizzy.crudebyte.com>) id 1jHaz4-0005A8-3e for qemu-devel@nongnu.org; Thu, 26 Mar 2020 18:28:19 -0400 Received: from lizzy.crudebyte.com ([91.194.90.13]:42819) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from <7c4e49a783c7b2f77aa81794892cf08b4feba914@lizzy.crudebyte.com>) id 1jHaz2-0004Dd-Dk for qemu-devel@nongnu.org; Thu, 26 Mar 2020 18:28:17 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=crudebyte.com; s=lizzy; h=Cc:To:Subject:Date:From:References:In-Reply-To: Message-Id:Content-Type:Content-Transfer-Encoding:MIME-Version:Content-ID: Content-Description; bh=jPdUMVvPDb49VGrJsLB5Dy+OTfiFUvEBcazVO3auyKA=; b=LmoSC KPt/p2vnLztv/ExKLe2NSSkJG4t/GCl8C3HNr8PV/3KzOyXDD2HSiOsFzSQkB82Wbz9eTekUo/o+f VNPd/8aYrK5G7M6AHujALQtPa+h4zCNYwZqzreZZ40EN0snWsXqySuW/KlZ6Tq71SBXuHH699/ecy F3gOIIhKfo/rqSbm0T8dQgW1Z9uuv0qTTerrwISHJGBz6eGtbh76FwYdOPyF0rOOtiXxv30KwOWH1 sH/CqMB3RCAbnVgPXyJ7IKWbEyKofceIYY/g1biIYFmvhQcvMmrMOO7WDY4rjF/B8JNVuBTiSq6k2 NP7PpIt1J+vVfPHwCEjYuplFoV1jg==; Message-Id: <7c4e49a783c7b2f77aa81794892cf08b4feba914.1585258105.git.qemu_oss@crudebyte.com> In-Reply-To: References: From: Christian Schoenebeck Date: Thu, 26 Mar 2020 22:25:32 +0100 Subject: [PATCH v5 6/6] 9pfs: clarify latency of v9fs_co_run_in_worker() To: qemu-devel@nongnu.org Cc: Greg Kurz X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 91.194.90.13 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: pass (identity @crudebyte.com) Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" As we just fixed a severe performance issue with Treaddir request handling, clarify this overall issue as a comment on v9fs_co_run_in_worker() with the intention to hopefully prevent such performance mistakes in future (and fixing other yet outstanding ones). Signed-off-by: Christian Schoenebeck --- hw/9pfs/coth.h | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/hw/9pfs/coth.h b/hw/9pfs/coth.h index a6851822d5..8b6f76840a 100644 --- a/hw/9pfs/coth.h +++ b/hw/9pfs/coth.h @@ -19,7 +19,7 @@ #include "qemu/coroutine.h" #include "9p.h" =20 -/* +/** * we want to use bottom half because we want to make sure the below * sequence of events. * @@ -28,6 +28,16 @@ * 3. Enter the coroutine in the worker thread. * we cannot swap step 1 and 2, because that would imply worker thread * can enter coroutine while step1 is still running + * + * @b PERFORMANCE @b CONSIDERATIONS: As a rule of thumb, keep in mind + * that hopping between threads adds @b latency! So when handling a + * 9pfs request, avoid calling v9fs_co_run_in_worker() too often, because + * this might otherwise sum up to a significant, huge overall latency for + * providing the response for just a single request. For that reason it + * is highly recommended to fetch all data from fs driver with a single + * fs driver request on a background I/O thread (bottom half) in one rush + * first and then eventually assembling the final response from that data + * on main I/O thread (top half). */ #define v9fs_co_run_in_worker(code_block) \ do { \ --=20 2.20.1