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 D16433FE4; Tue, 30 Jul 2024 20:05:53 +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=1722369955; cv=none; b=D8YjHOTX9dVLz0rUgF2t+QOdRwrYhIII2i5U+TwRat/8RIz2hVizUku3xOrfAElDpwdhwLMxVsOn1g/sAoyvCkueyoXSICVcNWzsA4ZGKDn6RyLS1W0NyXrkb/hwKIX+4b+XahQiJQ1hBl8GxpcVv5NrD7Ea6tMQYeyJg/AUzn8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722369955; c=relaxed/simple; bh=08Y5t+/8N2aBquIamx/IrSUR1vWd4M2XUzBHr2851tk=; h=Message-ID:Subject:From:To:Cc:Date:Content-Type:MIME-Version; b=Jy7r8m1dH+E4nEC2CY+d2fkrARQmMk2vahnWeukhxvv1S1ui4q8D3eSO03ug53PJLRpScnUtjSUGMsNW4VbJDp0GbHrb+uT3jyXyl8cAIRO7ftRhtfBL4iJgWFEyOk+lcZazf9Y+Tg5YVqfLbb0JTFAI37TjiQtbsHl8c9rFvw4= 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=53656 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 1sYt6W-0000cG-2X; Tue, 30 Jul 2024 16:05:52 -0400 Message-ID: Subject: io_uring NAPI busy poll RCU is causing 50 context switches/second to my sqpoll thread From: Olivier Langlois To: io-uring@vger.kernel.org Cc: netdev@vger.kernel.org Date: Tue, 30 Jul 2024 16:05:52 -0400 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 3.52.3 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: if you are interested into all the details, they are all here: https://github.com/axboe/liburing/issues/1190 it seems like I like to write a lot when I am investigating a problem. Pavel has been a great help in assisting me understanding what was happening. Next, I came to question where the integration of RCU came from and I have found this: https://lore.kernel.org/all/89ef84bf-48c2-594c-cc9c-f796adcab5e8@kernel.dk/ I guess that in some use-case being able to dynamically manage hundreds of NAPI devices automatically that can suddenly all be swepted over during a device reconfiguration is something desirable to have for some... but in my case, this is an excessively a high price to pay for a flexibility that I do not need at all. I have a single NAPI device. Once I know what it is, it will pratically remain immutable until termination. For that reason, I am thinking that offering some sort of polymorphic NAPI device tracking strategy customization would be desirable. The current one, the RCU one, I would call it the dynamic_napi_tracking (rcu could be peppered in the name somewhere so people know what the strategy is up to) where as the new one that I am imagining would be called static_napi_tracking. NAPI devices would be added/removed by the user manually through an extended registration function. for the sake of conveniance, a clear_list operation could even be offered. The benefits of this new static tracking strategy would be numerous: - this removes the need to invoke the heavy duty RCU cavalry - no need to scan the list to remove stall devices - no need to search the list at each SQE submission to update the device timeout value So is this a good idea in your opinion?