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Tue, 23 Jul 2024 13:15:04 -0400 X-MC-Unique: hVtQla4sNLq_bwaQT9zOmA-1 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (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-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 1BB2D1955D45; Tue, 23 Jul 2024 17:15:01 +0000 (UTC) Received: from tpad.localdomain (unknown [10.96.133.4]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 77132195605A; Tue, 23 Jul 2024 17:14:59 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id F2B23400DF27F; Tue, 23 Jul 2024 14:14:34 -0300 (-03) Date: Tue, 23 Jul 2024 14:14:34 -0300 From: Marcelo Tosatti To: Leonardo Bras Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Thomas Gleixner , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH v1 0/4] Introduce QPW for per-cpu operations Message-ID: References: <20240622035815.569665-1-leobras@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240622035815.569665-1-leobras@redhat.com> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 X-Stat-Signature: iz81raezg9xz4od1x1cuhjac3wz71nk8 X-Rspam-User: X-Rspamd-Queue-Id: 976B014000A X-Rspamd-Server: rspam02 X-HE-Tag: 1721754910-83515 X-HE-Meta: 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 vqgCQUPt lIv1h2qnsFUbJyfx+iX3c8xQ/dihxJMKmKjelUn19r7G4YH36HakidzmtX7HL5eWeUsl1ae8cjFK79aoP1IaE5q101EXPlsc0G/eyGFxlwofYtdTJloiTucporeWNWV/AocvMoN/DHXSq0BcZpSDMlWGFVbd1nIZ5b7/Nh+IfbxZYaiTpK2USMPKByrKLgOnq9mFqCQAeXLs5DGXYxvwffXxHgHVDhV/dqtBKxY0SpPNO2Zlfi6JxUF/P/QYS6/qZbKYCQhwCL3QMpse/HFJk6f5FD6uvX9xlsTKFD7wR9PfjZEZEO+NjqvkbX8fPL0/QtZvdstw9AZ8NFz4byqXiROBprAqXOfeUzFJbabDaG7L4K+E= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Jun 22, 2024 at 12:58:08AM -0300, Leonardo Bras wrote: > The problem: > Some places in the kernel implement a parallel programming strategy > consisting on local_locks() for most of the work, and some rare remote > operations are scheduled on target cpu. This keeps cache bouncing low since > cacheline tends to be mostly local, and avoids the cost of locks in non-RT > kernels, even though the very few remote operations will be expensive due > to scheduling overhead. > > On the other hand, for RT workloads this can represent a problem: getting > an important workload scheduled out to deal with remote requests is > sure to introduce unexpected deadline misses. Another hang with a busy polling workload (kernel update hangs on grub2-probe): [342431.665417] INFO: task grub2-probe:24484 blocked for more than 622 seconds. [342431.665458] Tainted: G W X ------- --- 5.14.0-438.el9s.x86_64+rt #1 [342431.665488] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [342431.665515] task:grub2-probe state:D stack:0 pid:24484 ppid:24455 flags:0x00004002 [342431.665523] Call Trace: [342431.665525] [342431.665527] __schedule+0x22a/0x580 [342431.665537] schedule+0x30/0x80 [342431.665539] schedule_timeout+0x153/0x190 [342431.665543] ? preempt_schedule_thunk+0x16/0x30 [342431.665548] ? preempt_count_add+0x70/0xa0 [342431.665554] __wait_for_common+0x8b/0x1c0 [342431.665557] ? __pfx_schedule_timeout+0x10/0x10 [342431.665560] __flush_work.isra.0+0x15b/0x220 [342431.665565] ? __pfx_wq_barrier_func+0x10/0x10 [342431.665570] __lru_add_drain_all+0x17d/0x220 [342431.665576] invalidate_bdev+0x28/0x40 [342431.665583] blkdev_common_ioctl+0x714/0xa30 [342431.665588] ? bucket_table_alloc.isra.0+0x1/0x150 [342431.665593] ? cp_new_stat+0xbb/0x180 [342431.665599] blkdev_ioctl+0x112/0x270 [342431.665603] ? security_file_ioctl+0x2f/0x50 [342431.665609] __x64_sys_ioctl+0x87/0xc0 [342431.665614] do_syscall_64+0x5c/0xf0 [342431.665619] ? __ct_user_enter+0x89/0x130 [342431.665623] ? syscall_exit_to_user_mode+0x22/0x40 [342431.665625] ? do_syscall_64+0x6b/0xf0 [342431.665627] ? __ct_user_enter+0x89/0x130 [342431.665629] entry_SYSCALL_64_after_hwframe+0x6e/0x76 [342431.665635] RIP: 0033:0x7f39856c757b [342431.665666] RSP: 002b:00007ffd9541c488 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [342431.665670] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f39856c757b [342431.665673] RDX: 0000000000000000 RSI: 0000000000001261 RDI: 0000000000000005 [342431.665674] RBP: 00007ffd9541c540 R08: 0000000000000003 R09: 006164732f766564 [342431.665676] R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffd9543ca68 [342431.665678] R13: 000055ea758a0708 R14: 000055ea759de338 R15: 00007f398586f000