From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from cloud48395.mywhc.ca (cloud48395.mywhc.ca [173.209.37.211]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0C0CA1EA84 for ; Tue, 13 Aug 2024 21:25:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=173.209.37.211 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723584354; cv=none; b=cnHOs6AAKSzeezjH1lSQeXPS6IIjRV1FryiY71tKSf4Ka6pBE+e3A4Qik8OA/66Fgw3pb0kfhg4A4t6v5z2k6yfqpI1L00fa5+CUKCjrgPIBeKFsHwjNLKntgH0u+a8iDIaRD3KeFlLAqrNGqnaa4TJy+06zYNPXMH3q1xBvopc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723584354; c=relaxed/simple; bh=xTJUiyNDRZERn7EjV6toWu7ACH3l+nGaWP43OCy1ZXg=; h=Message-ID:Subject:From:To:Date:In-Reply-To:References: Content-Type:MIME-Version; b=V3F8jKN7OOcXvFINNHD4oTxU/4n1DCdjcY2114ODOU4rx7uRboxpfoAyZ0il6R6RYBebIR+m3gRkMbgYYe7LiZyrzl82NzD1s34116KHsTLbhs6dQA0BxoLK+8FLFViQSwpmrV5YtM4B1d89qAI3ZgZYLfCcpWMlvTRV1rr8zyk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=trillion01.com; spf=pass smtp.mailfrom=trillion01.com; arc=none smtp.client-ip=173.209.37.211 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=trillion01.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=trillion01.com Received: from [45.44.224.220] (port=33394 helo=[192.168.1.177]) by cloud48395.mywhc.ca with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96.2) (envelope-from ) id 1sdz1U-0002F6-2D; Tue, 13 Aug 2024 17:25:44 -0400 Message-ID: Subject: Re: [PATCH 0/2] abstract napi tracking strategy From: Olivier Langlois To: Jens Axboe , Pavel Begunkov , io-uring@vger.kernel.org Date: Tue, 13 Aug 2024 17:25:43 -0400 In-Reply-To: References: Autocrypt: addr=olivier@trillion01.com; prefer-encrypt=mutual; keydata=mQINBFYd0ycBEAC53xedP1NExPwtBnDkVuMZgRiLmWoQQ8U7vEwt6HVGSsMRHx9smD76i 5rO/iCT6tDIpZoyJsTOh1h2NTn6ZkoFSn9lNOJksE77/n7HNaNxiBfvZHsuNuI53CkYFix9JhzP3t g5nV/401re30kRfA8OPivpnj6mZhU/9RTwjbVPPb8dPlm2gFLXwGPeDITgSRs+KJ0mM37fW8EatJs 0a8J1Nk8wBvT7ce+S2lOrxDItra9pW3ukze7LMirwvdMRC5bdlw2Lz03b5NrOUq+Wxv7szn5Xr9f/ HdaCH7baWNAO6H/O5LbJ3zndewokEmKk+oCIcXjaH0U6QK5gJoO+3Yt5dcTo92Vm3VMxzK2NPFXgp La7lR9Ei0hzQ0zptyFFyftt9uV71kMHldaQaSfUTsu9dJbnS2kI/j+F2S1q6dgKi3DEm0ZRGvjsSG rkgPJ5T16GI1cS2iQntawdr0A1vfXiB9xZ1SMGxL/l6js9BVlIx/CBGOJ4L190QmxJlcAZ2VnQzrl ramRUv01xb00IPJ5TBft5IJ+SY0FnY9pIERIl6w9khwLt/oGuKNmUHmzJGYoJHYfh72Mm8RQ1R/JS o6v85ULBGdEC3pQq1j//OPyH3egiXIwFq6BtULH5CvsxQkSqgj1MpjwfgVJ8VbjNwqwBXHjooEORj vFQqWQki6By3QARAQABtDJPbGl2aWVyIExhbmdsb2lzIChNeSBrZXkpIDxvbGl2aWVyQHRyaWxsaW 9uMDEuY29tPokCNwQTAQgAIQUCVh3TJwIbAwULCQgHAwUVCgkICwUWAgMBAAIeAQIXgAAKCRBlaka GGsWHEI1AD/9sbj+vnFU29WemVqB4iW+9RrHIcbXI4Jg8WaffTQ8KvVeCJ4otzgVT2nHC2A82t4PF 0tp21Ez17CKDNilMvOt8zq6ZHx36CPjoqUVjAdozOiBDpC4qB6ZKYn+gqSENO4hqmmaOW57wT9vII v6mtHmnFvgpOEJl6wbs8ArHDt0BLSjc8QQfvBhoKoWs+ijQTyvFGlQl0oWxEbUkR1J3gdft9Oj9xQ G4OFo73WaSEK/L9IalU2ulCBC+ucSP9McoDxy1i1u8HUDrV5wBY1zafc9zVBcMNH6+ZjxwQmZXqtz ATzB3RbSFHAdmvxl8q6MeS2yx7Atk0CXgW9z5k2KeuZhz5rVV5A+D19SSGzW11uYXsibZx/Wjr9xB KHB6U7qh5sRHaQS191NPonKcsXXAziR+vxwQTP7ZKfy+g5N/e6uivoUnQrl9uvUDDPXEpwVNSoVws Vn4tNyrGEdN11pHDbH5fSGzdpbY8+yczUoxMmsEQe/fpVwRBZUqafRn2TVUhV0qqzsUuQcTNw1zIZ JgvkqrHgd4ivd2b1bXBczmu/wMGpEnF6cWzSQDiwC1NF3i+gHCuD8IX1ujThWtzXsn0VtrMkrRCbn ponVQ6HcbRYYXPuK0HRRjCSuAKo5porVONepiOSmu0FBrpGqBkpBtLrzKXoi1yt/7a/wGdMcVhYGg vA== Organization: Trillion01 Inc Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.52.4 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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: On Tue, 2024-08-13 at 12:33 -0600, Jens Axboe wrote: > On 8/13/24 10:44 AM, Olivier Langlois wrote: > > the actual napi tracking strategy is inducing a non-negligeable > > overhead. > > Everytime a multishot poll is triggered or any poll armed, if the > > napi is > > enabled on the ring a lookup is performed to either add a new napi > > id into > > the napi_list or its timeout value is updated. > >=20 > > For many scenarios, this is overkill as the napi id list will be > > pretty > > much static most of the time. To address this common scenario, a > > new > > abstraction has been created following the common Linux kernel > > idiom of > > creating an abstract interface with a struct filled with function > > pointers. > >=20 > > Creating an alternate napi tracking strategy is therefore made in 2 > > phases. > >=20 > > 1. Introduce the io_napi_tracking_ops interface > > 2. Implement a static napi tracking by defining a new > > io_napi_tracking_ops >=20 > I don't think we should create ops for this, unless there's a strict > need to do so. Indirect function calls aren't cheap, and the CPU side > mitigations for security issues made them worse. >=20 > You're not wrong that ops is not an uncommon idiom in the kernel, but > it's a lot less prevalent as a solution than it used to. Exactly > because > of the above reasons. >=20 ok. Do you have a reference explaining this? and what type of construct would you use instead? AFAIK, a big performance killer is the branch mispredictions coming from big switch/case or if/else if/else blocks and it was precisely the reason why you removed the big switch/case io_uring was having with function pointers in io_issue_def... I consumme an enormous amount of programming learning material daily and this is the first time that I am hearing this. If there was a performance concern about this type of construct and considering that my main programming language is C++, I am bit surprised that I have not seen anything about some problems with C++ vtbls... but oh well, I am learning new stuff everyday, so please share the references you have about the topic so that I can perfect my knowledge. thank you,