From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) (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 6F8D138396 for ; Thu, 10 Oct 2024 15:14:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=96.67.55.147 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728573252; cv=none; b=dqGcpxOeuapE3XdPSm/h2y+3O6ne3lSOQfDziT89XhLMWSnP0vqPB3wQlfeej4K4fXj36wWy8EycV7gFjHE31F2MQK4erNDarM6XcTAenabnuEVYczXt2knPl83DiRxuULLoGd9CH3hK1rlPyRnZTqWOtBBhM2g3PjpJbMN7fDk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728573252; c=relaxed/simple; bh=PQi3BZ57ldSTBUX1M6ILSrh846FLe9rXTg8aDmLJs6E=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=s9FCQ1kfBmjBNVBwnkIw5GhbWENEMAD6spk5zKv/mKOlDi16SwCg3ISNgzkdkQf2bpwZX73mSzAag9kJ47it7NUjo8Whh6dMR9CIV21wIkGooDsideQs8EHdmdOIlCahpi+WNjS3ozBJ7gvwIJNIMp5+YrT9AwnhnsVGmCHp4GM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=surriel.com; spf=pass smtp.mailfrom=shelob.surriel.com; arc=none smtp.client-ip=96.67.55.147 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=surriel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=shelob.surriel.com Received: from [2601:18c:9101:a8b6:6e0b:84ff:fee2:98bb] (helo=imladris.surriel.com) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.97.1) (envelope-from ) id 1syur9-000000003gD-2sEK; Thu, 10 Oct 2024 11:13:35 -0400 Message-ID: <9ca16991fa83fb7c7baeee153666d70717be2b7a.camel@surriel.com> Subject: Re: locking/csd-lock: Switch from sched_clock() to ktime_get_mono_fast_ns() From: Rik van Riel To: paulmck@kernel.org, linux-kernel@vger.kernel.org Cc: neeraj.upadhyay@kernel.org, leobras@redhat.com, tglx@linutronix.de, peterz@infradead.org, qiyuzhu2@amd.com Date: Thu, 10 Oct 2024 11:13:35 -0400 In-Reply-To: References: Autocrypt: addr=riel@surriel.com; prefer-encrypt=mutual; keydata=mQENBFIt3aUBCADCK0LicyCYyMa0E1lodCDUBf6G+6C5UXKG1jEYwQu49cc/gUBTTk33Aeo2hjn4JinVaPF3zfZprnKMEGGv4dHvEOCPWiNhlz5RtqH3SKJllq2dpeMS9RqbMvDA36rlJIIo47Z/nl6IA8MDhSqyqdnTY8z7LnQHqq16jAqwo7Ll9qALXz4yG1ZdSCmo80VPetBZZPw7WMjo+1hByv/lvdFnLfiQ52tayuuC1r9x2qZ/SYWd2M4p/f5CLmvG9UcnkbYFsKWz8bwOBWKg1PQcaYHLx06sHGdYdIDaeVvkIfMFwAprSo5EFU+aes2VB2ZjugOTbkkW2aPSWTRsBhPHhV6dABEBAAG0HlJpayB2YW4gUmllbCA8cmllbEByZWRoYXQuY29tPokBHwQwAQIACQUCW5LcVgIdIAAKCRDOed6ShMTeg05SB/986ogEgdq4byrtaBQKFg5LWfd8e+h+QzLOg/T8mSS3dJzFXe5JBOfvYg7Bj47xXi9I5sM+I9Lu9+1XVb/r2rGJrU1DwA09TnmyFtK76bgMF0sBEh1ECILYNQTEIemzNFwOWLZZlEhZFRJsZyX+mtEp/WQIygHVWjwuP69VJw+fPQvLOGn4j8W9QXuvhha7u1QJ7mYx4dLGHrZlHdwDsqpvWsW+3rsIqs1BBe5/Itz9o6y9gLNtQzwmSDioV8KhF85VmYInslhv5tUtMEppfdTLyX4SUKh8ftNIVmH9mXyRCZclSoa6IMd635Jq1Pj2/Lp64tOzSvN5Y9zaiCc5FucXtB9SaWsgdmFuIFJpZWwgPHJpZWxAc3VycmllbC5jb20+iQE+BBMBAgAoBQJSLd2lAhsjBQkSzAMABgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAAKCRDOed6ShMTeg4PpB/0ZivKYFt0LaB22ssWUrBoeNWCP1NY/lkq2QbPhR3agLB7ZXI97PF2z/5QD9Fuy/FD/j 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.4 (3.50.4-1.fc39) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Sender: riel@surriel.com On Wed, 2024-10-09 at 10:57 -0700, Paul E. McKenney wrote: > Currently, the CONFIG_CSD_LOCK_WAIT_DEBUG code uses sched_clock() > to check for excessive CSD-lock wait times.=C2=A0 This works, but does no= t > guarantee monotonic timestamps.=C2=A0 Therefore, switch from sched_clock(= ) > to ktime_get_mono_fast_ns(), which does guarantee monotonic > timestamps, > at least in the absence of calls from NMI handlers, which are not > involved > in this code path. >=20 > Signed-off-by: Paul E. McKenney > Cc: Neeraj Upadhyay > Cc: Rik van Riel > Cc: Leonardo Bras > Cc: Thomas Gleixner > Cc: "Peter Zijlstra (Intel)" The functional change here is that sched_clock() uses rdtsc(), while ktime_get_mono_fast_ns() uses rdtsc_ordered(). I don't know if sched_clock() should also be using rdtsc_ordered(). Reviewed-by: Rik van Riel --=20 All Rights Reversed.