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X-BeenThere: linux-mediatek@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-mediatek" Errors-To: linux-mediatek-bounces+linux-mediatek=archiver.kernel.org@lists.infradead.org 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