From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id AC2D0C4332F for ; Mon, 6 Nov 2023 20:40:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Date:Cc:To:From:Subject:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=T7sbufs5kTTgM2R9JcgvUSie3u/C96Nvhjslts5OeVc=; b=xKUnuXU8iigH61 Yqx86mSHIZad63xzcjlWwuau6tn4KOTKS7xSBBYaVDD9hq04gpIsOf+UUi38w02s0QezgeQlVnA6x k3Anh9MHqnT+6RJpGYR+zbPtK6AAm04ISiRoenPTTKIkGJ9DpQdqT4HBTJMBZJGy/t5/dJ9O0yOXO +e3QOABFHdgoycoDY5c3t9To4rA1iwXO49lKF9kOSB7WJjIVEl/H9ltcw8LjI1I8qwQLk4vHnDkgZ gZ/jjWVM9LIwrqiU7fMybr44PRcLkQ4Tq1ogQimDDtfj00SHy6XYk6FPJ0t86JLTIqM6wYP9HaKLC +IeR9GpucYcVKoh/uipQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1r06OP-00HWCE-0t; Mon, 06 Nov 2023 20:40:17 +0000 Received: from s3.sipsolutions.net ([2a01:4f8:242:246e::2] helo=sipsolutions.net) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1r06OM-00HWA7-2L for linux-um@lists.infradead.org; Mon, 06 Nov 2023 20:40:16 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sipsolutions.net; s=mail; h=MIME-Version:Content-Transfer-Encoding: Content-Type:References:In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender :Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From:Resent-To: Resent-Cc:Resent-Message-ID; bh=LV4SaRoVTeYXOUa0lriFjTOhuj7g4S8hXczoP7gmiPo=; t=1699303211; x=1700512811; b=HC2nKx+PMkefQ2HJuZQNq1ca7B6Prwa3M69OsXLg6KJyxfc zQlfZvZyl0mhhS7kOHLICUOyH2hBRJ90e7j74IUhWv9cJf9kni2eP6GxoOVWF7IuidYXTufYiRZlw uMz/eumgMD4xecTzT1rz/xF184oCBMq2xLsS3fUoIwmsn3+ehMK8+mSdosavA8D2mVB91/1ApW0Dt 8K1GxXfeCSyTL5nHBx4Xdopn+QP4oiKc+73IIXGuoKMKhMSla9Ihc4Ndu5BBKlVTMOiMLj86kCyRj /0qyF+M5o3WR6e8BQk6jOKzJmESOTAbsy51jDpw6XzGYwEaeky1JBP5WUDRELZ2A==; Received: by sipsolutions.net with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.97-RC1) (envelope-from ) id 1r06OC-0000000FtDG-1kQu; Mon, 06 Nov 2023 21:40:04 +0100 Message-ID: Subject: Re: [PATCH RFC 09/11] um: Delay timer_read in time travel mode only after consecutive reads From: Johannes Berg To: Benjamin Beichler , Richard Weinberger , Anton Ivanov Cc: linux-um@lists.infradead.org Date: Mon, 06 Nov 2023 21:40:03 +0100 In-Reply-To: <20231103-bb-timetravel-patches-v1-9-e2c68efcf664@uni-rostock.de> References: <20231103-bb-timetravel-patches-v1-0-e2c68efcf664@uni-rostock.de> <20231103-bb-timetravel-patches-v1-9-e2c68efcf664@uni-rostock.de> User-Agent: Evolution 3.48.4 (3.48.4-1.fc38) MIME-Version: 1.0 X-malware-bazaar: not-scanned X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231106_124014_772484_2EE0799F X-CRM114-Status: UNSURE ( 8.83 ) X-CRM114-Notice: Please train this message. X-BeenThere: linux-um@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-um" Errors-To: linux-um-bounces+linux-um=archiver.kernel.org@lists.infradead.org On Fri, 2023-11-03 at 16:41 +0000, Benjamin Beichler wrote: > Given the presence of numerous timer_read calls in well-behaved code > within the kernel and userspace, particularly those that do not employ > busy loops, we introduce a delay in reading the timer only after several > consecutive attempts (currently set at 10). > > Unfortunately, it is challenging to differentiate between various > callers and pinpoint specific misbehaving code, so this is only a > mediocre heuristic. Could use with some more comments in the code I guess. :) Generally I'd say what we have now isn't a _problem_, but in a sense if you implement infinite CPU speed ... why does reading the time take time? Not that I think it's _wrong_, and arguably you always should've expected reading time to take time, but ... Arguably though this should be squashed with the next patch since you restrict it there? johannes _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um