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 26582200113 for ; Mon, 19 Jan 2026 10:47:12 +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=1768819634; cv=none; b=kV9Ns8ETy7r5TFb5RZmeDJ/UMxGMzjzce4eaGef2Al5Sm5B4jwrQa85GMSx0SIhKEMGwpKbzQodnainfE/oS5pxkbRwVQnu/v/YYRU9M+JAng3kI653QdwRVEVwUtHaMHc07D+BzYAzvOLLvesHlyT9e9h/N2lI3lVUcrKY61j8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768819634; c=relaxed/simple; bh=lbSm9dCStmZlmyPftoxBVs6faUaWFkAG38XKclkCSWk=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=ucmWvI6/6oQY6F8ppc93nfJ62ypK2XFN0ZdCP5tl6bi6xMf2BkSVkJcKRBa7hknw6YGpkzOPZHY9SATm337GPfKFqUkg6Yi5PI3gSyevuJmmN+8jR/GCkcllSrXGZ/jCQ+fF8Toi6CzUxnjwu6pAZqB/KCdtRitrv56S3/l8uik= 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=Dcez2PzV; 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="Dcez2PzV" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1768819632; 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: in-reply-to:in-reply-to:references:references; bh=NkTfYTOgyDyq9zTC+QFnQk1zBEkgtIki928ZacAuUck=; b=Dcez2PzVaj02lXduufdXOvMa0+ongoJEmK8KMGHhFM8hYHnN3kn6KhBti8wKy4EJ0sOb41 O3Lpjv+B50NsqDqI32QhFmwKKy1vfwzjaEspJtyDI1E+A+cc8TNick5rgfdkvj2xwEwdAO XGQXQ8TXNkvAxbsBO/9Q0T1JkESfMxY= Received: from mx-prod-mc-08.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-690-HUsZb-C1OhKeap8G5KrJlA-1; Mon, 19 Jan 2026 05:47:08 -0500 X-MC-Unique: HUsZb-C1OhKeap8G5KrJlA-1 X-Mimecast-MFC-AGG-ID: HUsZb-C1OhKeap8G5KrJlA_1768819626 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5069F1800357; Mon, 19 Jan 2026 10:47:05 +0000 (UTC) Received: from fweimer-oldenburg.csb.redhat.com (unknown [10.44.32.41]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 89E0819560AB; Mon, 19 Jan 2026 10:46:58 +0000 (UTC) From: Florian Weimer To: Peter Zijlstra Cc: Mathieu Desnoyers , Thomas Gleixner , LKML , "Paul E. McKenney" , Boqun Feng , Jonathan Corbet , Prakash Sangappa , Madadi Vineeth Reddy , K Prateek Nayak , Steven Rostedt , Sebastian Andrzej Siewior , Arnd Bergmann , linux-arch@vger.kernel.org, Randy Dunlap , Ron Geva , Waiman Long , "carlos@redhat.com" , Michael Jeanson Subject: Re: [patch V6 01/11] rseq: Add fields and constants for time slice extension In-Reply-To: <20260119102138.GQ830755@noisy.programming.kicks-ass.net> (Peter Zijlstra's message of "Mon, 19 Jan 2026 11:21:38 +0100") References: <20251215155615.870031952@linutronix.de> <20251215155708.669472597@linutronix.de> <87jyyjbclh.ffs@tglx> <225b9868-4ab7-4a90-8acb-8d965626f6a7@efficios.com> <87ldi4gjm3.ffs@tglx> <45fd706a-86be-42b8-879e-11bbe262e159@efficios.com> <20260119102138.GQ830755@noisy.programming.kicks-ass.net> Date: Mon, 19 Jan 2026 11:46:56 +0100 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 * Peter Zijlstra: > On Sat, Jan 17, 2026 at 05:16:16PM +0100, Mathieu Desnoyers wrote: > >> My main concern is about the overhead of added system calls at thread >> creation. I recall that doing an additional rseq system call at thread >> creation was analyzed thoroughly for performance regressions at the >> libc level. I would not want to start requiring libc to issue a >> handful of additional prctl system calls per thread creation for no good >> reason. > > A wee something like so? > > That would allow registering rseq with RSEQ_FLAG_SLICE_EXT_DEFAULT_ON > set and if all the stars align, it will then have it on at the end. I think this would work for glibc because it will only show up in __rseq_flags if we set the flag on process startup, and then all threads would get it. It doesn't matter that __rseq_flags is not per-thread. Thanks, Florian