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 3A9F619F130 for ; Mon, 14 Apr 2025 12:36:53 +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=1744634216; cv=none; b=eRLdPzf8DYDMYoZz8NsT52YFsJqXn2lbgAWsLM8PRLoHjmE3Z0E01zIyrjYaTgi6XDqXqZUtYBBZN7aP6CRPv6ksSn+IGq3zgyrYqM6AXw+ENzGmC/nPFOiPSF53xo0hHi+ohFF0IK5NehDdByyypuDjcwwkFXfu6SqgyNz4SLg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744634216; c=relaxed/simple; bh=Tox8nJJxpNhdC4ugPtgfSxfw0a1t3wyqBFmFaNDKtrA=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=Av5yZ3cmCPrw0lO4lQZvYcmMHjjJNbSdqJvC028SsxLCwy1ExA7Oqw2b9ahIz09teuTnmDWc2kBgfQ2XrlSnVgf7nyu4IlKxL8cJ0YauhyadDy5ICta3G29FbvEr6fTt9r0TY1F123HB5zonYjKeMjSIRrugtxvV07cj+SJ+DyA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine 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=SAbb4ycG; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine 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="SAbb4ycG" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1744634213; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=5MYOswkZT8OHdkgDSgQ80FWXuY4sOXJuxE2O8/5HgQA=; b=SAbb4ycG2ws4Rh2Qn0YBk8mWXQ+A2xJgo7PWMFk+f01sH89tYGdfNkP7OcVMw5G6OHK+Uq AjW9poBk2j3mbgqwUD+sOo1Vp3iyh3Glb2juw4KqxbUYSgdV4QUFEfiKxcPtIFpqD29AfB SkWn2Bp1TubqSrBVv2OLO4ABdgDRRQ8= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-616-JCEVhklKObumtBhboqJ0MQ-1; Mon, 14 Apr 2025 08:36:51 -0400 X-MC-Unique: JCEVhklKObumtBhboqJ0MQ-1 X-Mimecast-MFC-AGG-ID: JCEVhklKObumtBhboqJ0MQ_1744634210 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (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-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 4E13818001E2; Mon, 14 Apr 2025 12:36:50 +0000 (UTC) Received: from gmonaco-thinkpadt14gen3.rmtit.com (unknown [10.45.225.177]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id C20C2180B487; Mon, 14 Apr 2025 12:36:47 +0000 (UTC) From: Gabriele Monaco To: linux-kernel@vger.kernel.org, "To: Mathieu Desnoyers" , "To: Peter Zijlstra" , "To: Ingo Molnar" Cc: Gabriele Monaco Subject: [PATCH v13 0/3] sched: Restructure task_mm_cid_work for predictability Date: Mon, 14 Apr 2025 14:36:31 +0200 Message-ID: <20250414123630.177385-5-gmonaco@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 This patchset moves the task_mm_cid_work to a preemptible and migratable context. This reduces the impact of this work to the scheduling latency of real time tasks. The change makes the recurrence of the task a bit more predictable. The behaviour causing latency was introduced in commit 223baf9d17f2 ("sched: Fix performance regression introduced by mm_cid") which introduced a task work tied to the scheduler tick. That approach presents two possible issues: * the task work runs before returning to user and causes, in fact, a scheduling latency (with order of magnitude significant in PREEMPT_RT) * periodic tasks with short runtime are less likely to run during the tick, hence they might not run the task work at all Patch 1 add support for prev_sum_exec_runtime to the RT, deadline and sched_ext classes as it is supported by fair, this is required to avoid calling rseq_preempt on tick if the runtime is below a threshold. Patch 2 contains the main changes, removing the task_work on the scheduler tick and using a work_struct scheduled more reliably during __rseq_handle_notify_resume. Patch 3 adds a selftest to validate the functionality of the task_mm_cid_work (i.e. to compact the mm_cids). Changes since V12: * Ensure the tick schedules the mm_cid compaction only once for tasks executing longer than 100ms (until the scan expires again) * Execute an rseq_preempt from the tick only after compaction was done and the cid assignation changed Changes since V11: * Remove variable to make mm_cid_needs_scan more compact * All patches reviewed Changes since V10: * Fix compilation errors with RSEQ and/or MM_CID disabled Changes since V9: * Simplify and move checks from task_queue_mm_cid to its call site Changes since V8 [1]: * Add support for prev_sum_exec_runtime to RT, deadline and sched_ext * Avoid rseq_preempt on ticks unless executing for more than 100ms * Queue the work on the unbound workqueue Changes since V7: * Schedule mm_cid compaction and update at every tick too * mmgrab before scheduling the work Changes since V6 [2]: * Switch to a simple work_struct instead of a delayed work * Schedule the work_struct in __rseq_handle_notify_resume * Asynchronously disable the work but make sure mm is there while we run * Remove first patch as merged independently * Fix commit tag for test Changes since V5: * Punctuation Changes since V4 [3]: * Fixes on the selftest * Polished memory allocation and cleanup * Handle the test failure in main Changes since V3 [4]: * Fixes on the selftest * Minor style issues in comments and indentation * Use of perror where possible * Add a barrier to align threads execution * Improve test failure and error handling Changes since V2 [5]: * Change the order of the patches * Merge patches changing the main delayed_work logic * Improved self-test to spawn 1 less thread and use the main one instead Changes since V1 [6]: * Re-arm the delayed_work at each invocation * Cancel the work synchronously at mmdrop * Remove next scan fields and completely rely on the delayed_work * Shrink mm_cid allocation with nr thread/affinity (Mathieu Desnoyers) * Add self test [1] - https://lore.kernel.org/lkml/20250220102639.141314-1-gmonaco@redhat.com [2] - https://lore.kernel.org/lkml/20250210153253.460471-1-gmonaco@redhat.com [3] - https://lore.kernel.org/lkml/20250113074231.61638-4-gmonaco@redhat.com [4] - https://lore.kernel.org/lkml/20241216130909.240042-1-gmonaco@redhat.com [5] - https://lore.kernel.org/lkml/20241213095407.271357-1-gmonaco@redhat.com [6] - https://lore.kernel.org/lkml/20241205083110.180134-2-gmonaco@redhat.com To: Mathieu Desnoyers To: Peter Zijlstra To: Ingo Molnar Gabriele Monaco (3): sched: Add prev_sum_exec_runtime support for RT, DL and SCX classes sched: Move task_mm_cid_work to mm work_struct selftests/rseq: Add test for mm_cid compaction include/linux/mm_types.h | 26 +++ include/linux/sched.h | 8 +- kernel/rseq.c | 2 + kernel/sched/core.c | 75 ++++--- kernel/sched/deadline.c | 1 + kernel/sched/ext.c | 1 + kernel/sched/rt.c | 1 + kernel/sched/sched.h | 6 +- tools/testing/selftests/rseq/.gitignore | 1 + tools/testing/selftests/rseq/Makefile | 2 +- .../selftests/rseq/mm_cid_compaction_test.c | 200 ++++++++++++++++++ 11 files changed, 294 insertions(+), 29 deletions(-) create mode 100644 tools/testing/selftests/rseq/mm_cid_compaction_test.c base-commit: 8ffd015db85fea3e15a77027fda6c02ced4d2444 -- 2.49.0