From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C612AC433EF for ; Tue, 15 Feb 2022 18:05:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233361AbiBOSFW (ORCPT ); Tue, 15 Feb 2022 13:05:22 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:43296 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236250AbiBOSFW (ORCPT ); Tue, 15 Feb 2022 13:05:22 -0500 Received: from cloud48395.mywhc.ca (cloud48395.mywhc.ca [173.209.37.211]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9288BC1146 for ; Tue, 15 Feb 2022 10:05:11 -0800 (PST) Received: from [45.44.224.220] (port=44310 helo=[192.168.1.179]) by cloud48395.mywhc.ca with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1nK2CM-0004B7-K3; Tue, 15 Feb 2022 13:05:10 -0500 Message-ID: Subject: Re: napi_busy_poll From: Olivier Langlois To: Hao Xu , Jens Axboe , io-uring@vger.kernel.org Date: Tue, 15 Feb 2022 13:05:09 -0500 In-Reply-To: <995e65ce3d353cacea4d426c9876b2a5e88faa99.camel@trillion01.com> References: <21bfe359aa45123b36ee823076a036146d1d9518.camel@trillion01.com> <0446f39d-f926-0ae4-7ea4-00aff9236322@linux.alibaba.com> <995e65ce3d353cacea4d426c9876b2a5e88faa99.camel@trillion01.com> Organization: Trillion01 Inc Content-Type: text/plain; charset="ISO-8859-1" User-Agent: Evolution 3.42.3 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - cloud48395.mywhc.ca X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - trillion01.com X-Get-Message-Sender-Via: cloud48395.mywhc.ca: authenticated_id: olivier@trillion01.com X-Authenticated-Sender: cloud48395.mywhc.ca: olivier@trillion01.com X-Source: X-Source-Args: X-Source-Dir: Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Tue, 2022-02-15 at 03:37 -0500, Olivier Langlois wrote: > > That being said, I have not been able to make it work yet. For some > unknown reasons, no valid napi_id is extracted from the sockets added > to the context so the net_busy_poll function is never called. > > I find that very strange since prior to use io_uring, my code was > using > epoll and the busy polling was working fine with my application > sockets. Something is escaping my comprehension. I must tired and > this > will become obvious... > The napi_id values associated with my sockets appear to be in the range 0 < napi_id < MIN_NAPI_ID from busy_loop.h: /* 0 - Reserved to indicate value not set * 1..NR_CPUS - Reserved for sender_cpu * NR_CPUS+1..~0 - Region available for NAPI IDs */ #define MIN_NAPI_ID ((unsigned int)(NR_CPUS + 1)) I have found this: https://lwn.net/Articles/619862/ hinting that busy_poll may be incompatible with RPS (Documentation/networking/scaling.rst) that I may have discovered *AFTER* my epoll -> io_uring transition (I don't recall exactly the sequence of my learning process). With my current knowledge, it makes little sense why busy polling would not be possible with RPS. Also, what exactly is a NAPI device is quite nebulous to me... Looking into the Intel igb driver code, it seems like 1 NAPI device is created for each interrupt vector/Rx buffer of the device. Bottomline, it seems like I have fallen into a new rabbit hole. It may take me a day or 2 to figure it all... you are welcome to enlight me if you know a thing or 2 about those topics... I am kinda lost right now...