From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 B7E32111A8 for ; Wed, 17 Jul 2024 18:55:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721242555; cv=none; b=CXxEMEYWGapzgCVg4gNmvLGHgYHYBJechL9ZVADoUet5LJlMdwRjghHr5ukUzwjZaHEmusVXgXTcwk8lhx3T3MAguKc/l/kx6IZXfBWSQt5m/6vkW+67fK1N+b7io3A/dUSD5stkLmyvGQIVhH+j2zPpTG9Q3mop9tdDC1XeGGY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721242555; c=relaxed/simple; bh=1ypNYqyJd5+/3wMS25bBg2wSCYkGAoz3khgoCCUzXvU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=BaEmtndcD/TE0TiqJ94n7G5MUUOaGKOy3fQE81rrH4X5gPU6CxndzObvL/OdjGa/cnRpEP5BhFIoQv6UZiLgixPBDUUN4LOWOAKhFYhRQKbTX2PfBCJ306A6RYlzTk1xFG1pgy/cM4KI06CoU9D3jzNym3ZazZ0ori9xoC3tjrM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=NEkqHf0x; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="NEkqHf0x" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1721242552; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=42DJEZQ1MdHTtg7QJxt70aly4kDVOHsjcs6e6lW7JWQ=; b=NEkqHf0x1ZO+bOGP0K+4Zta+okc6jY0bMKdZ5lkem/3PD4JJ3UvKGXiztovSLRf0I39Tuu 10CJBuwCUB6Zj9KPi0+WVA+joQ/2JXlzXYaBvWo4K1C2s+MNqDb2hufX+EXE8fN412JDap 3iD0KzB6xUeL3fPA2Pge5Y3W1Yc6vEc= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-510-GJ8a38dFOd6eX2lsh8TOXQ-1; Wed, 17 Jul 2024 14:55:48 -0400 X-MC-Unique: GJ8a38dFOd6eX2lsh8TOXQ-1 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 899E01979058; Wed, 17 Jul 2024 18:55:41 +0000 (UTC) Received: from [10.22.16.209] (unknown [10.22.16.209]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 696931955F21; Wed, 17 Jul 2024 18:55:38 +0000 (UTC) Message-ID: <48fa8bc9-9f8d-4406-9137-88a555883ea2@redhat.com> Date: Wed, 17 Jul 2024 14:55:37 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] blk-cgroup: Replace u64 sync with spinlock for iostat update To: "tj@kernel.org" Cc: =?UTF-8?B?Qm95IFd1ICjlkLPli4Poqrwp?= , "boris@bur.io" , "linux-block@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "cgroups@vger.kernel.org" , "linux-mediatek@lists.infradead.org" , "axboe@kernel.dk" , =?UTF-8?B?SXZlcmxpbiBXYW5nICjnjovoi7PpnJYp?= , "josef@toxicpanda.com" , "linux-arm-kernel@lists.infradead.org" , "matthias.bgg@gmail.com" , "angelogioacchino.delregno@collabora.com" References: <20240716075206.23121-1-boy.wu@mediatek.com> <5560c690cc6de67139a9b2e45c7a11938b70fc58.camel@mediatek.com> <1b19b68adb34410bf6dc8fd3f50e4b82c1a014e4.camel@mediatek.com> <134fc34c-10b8-4d00-aaca-8285efce9899@redhat.com> Content-Language: en-US From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 On 7/17/24 14:24, tj@kernel.org wrote: > Hello, > > On Wed, Jul 17, 2024 at 02:18:39PM -0400, Waiman Long wrote: >> Well, it can be confusing whether we are dealing with blkg->iostat or >> blkg->iostat_cpu. In many cases, we are dealing with iostat_cpu instead of >> iostat like __blkcg_rstat_flush() and blkg_clear_stat(). So we can't >> eliminate the use of u64_stats_update_begin_irqsave() in those cases. > I mean, we need to distinguish them. For 32bits, blkg->iostat has multiple > updaters, so we can't use u64_sync; however, blkg->iostat_cpu has only one > updater (except blkg_clear_stat() which I don't think we need to worry too > much about), so u64_sync is fine. I was wrong about __blkcg_rstat_flush(). Right, the main updater of iostat_cpu is  blk_cgroup_bio_start(). We do need to drop down some comment on what is protected by u64_sync and what is by blkg_stat_lock though. It can be confusing. Cheers, Longman