From nobody Mon Feb 9 16:53:56 2026 Delivered-To: importer@patchew.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=1597236435; cv=none; d=zohomail.com; s=zohoarc; b=XLoB9mTEafznubUUYtLVykELbgL6bj9g3SUPAhdCQIVtdVL0NrBGTQlgMo/pEQiU2EXqQWZh8rASFnIhWY7uxRoricKzQ2tojdwoqfUGYw+axeeRBQ+aECBAlPKNQFOZlmceh8nYy6MUj0e4dwsqRTeL8q3ruUGPej6W4prNgMQ= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1597236435; 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=iIOY7lnyCREAN0i5cfmgv+fsotclpHEmOG5eXJ6R0b4=; b=nSrGG8DVXLjlnjRxtla7qY8rFDt1tGmT19vwtcero/ioPVkWkO2A41R2yiJGjieWKndufB8KKm+ZPj3/jveiygpYlOKJn2eo2e6lxhcHiVEbqdhhEek/28F8skl4PTrbCWoRloPVDp1PazXyGIjk2JZ0c4MgLDuw7okdCXA7D28= 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 1597236435451336.60020526367566; Wed, 12 Aug 2020 05:47:15 -0700 (PDT) Received: from localhost ([::1]:59988 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1k5q9x-0000wk-RK for importer@patchew.org; Wed, 12 Aug 2020 08:47:13 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:35384) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k5q8n-000881-77 for qemu-devel@nongnu.org; Wed, 12 Aug 2020 08:46:01 -0400 Received: from lizzy.crudebyte.com ([91.194.90.13]:56265) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k5q8l-0005fu-Mx for qemu-devel@nongnu.org; Wed, 12 Aug 2020 08:46:00 -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=iIOY7lnyCREAN0i5cfmgv+fsotclpHEmOG5eXJ6R0b4=; b=bUaJf QqLeGuM9Nl6kcIvVz0EEH5Oa0xRx+FlHzuB9DFykCI4ANl5Uvsa73OSIjgwfzvT3ZjwH37R0XjZHJ Lnv/kP2hHWh6fn2Cm8J2owNIRQZNMJl800RtiTUSP2DKq1w5O7m3eXCohEiIVI0i0QYlHDFXaTazo /kRqFBTh+MAHE81gSNgFW87uyIm5ybsd/ZwwYrbOYR9Gw+jeeO8egdhFhXSyuTi3P1VzXPocia8xU t+kjAGG2Hq6x18AWCrSLVslOAIXzfvj8ihdleTcuKipmE1iX4iU5W5Tq+QYBuTIvB9WuyXOz/7MHb l1wuu9xx1N+u+eXSdpN8O63AThyxQ==; Message-Id: In-Reply-To: References: From: Christian Schoenebeck Date: Wed, 29 Jul 2020 10:42:28 +0200 Subject: [PULL 7/7] 9pfs: clarify latency of v9fs_co_run_in_worker() To: qemu-devel@nongnu.org, Peter Maydell Cc: Greg Kurz 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; Received-SPF: none client-ip=91.194.90.13; envelope-from=da9f2eda2551c1cbd98f72730e5b754f2149a85c@lizzy.crudebyte.com; helo=lizzy.crudebyte.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/12 08:16:56 X-ACL-Warn: Detected OS = Linux 3.11 and newer X-Spam_score_int: 13 X-Spam_score: 1.3 X-Spam_bar: + X-Spam_report: (1.3 / 5.0 requ) BAYES_00=-1.9, DATE_IN_PAST_96_XX=3.405, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_NONE=0.001, URIBL_BLOCKED=0.001 autolearn=no autolearn_force=no X-Spam_action: no action 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 Message-Id: <4d34d332e1aaa8a2cf8dc0b5da4fd7727f2a86e8.1596012787.git.qemu_o= ss@crudebyte.com> 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 fd4a45bc7c..c51289903d 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