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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 27BA7C433EF for ; Wed, 24 Nov 2021 21:20:03 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A010D6B0075; Wed, 24 Nov 2021 16:19:47 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 9AFD66B0078; Wed, 24 Nov 2021 16:19:47 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 878286B007B; Wed, 24 Nov 2021 16:19:47 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0020.hostedemail.com [216.40.44.20]) by kanga.kvack.org (Postfix) with ESMTP id 78DE06B0075 for ; Wed, 24 Nov 2021 16:19:47 -0500 (EST) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 41180182C04D4 for ; Wed, 24 Nov 2021 21:19:37 +0000 (UTC) X-FDA: 78845090394.21.B9F21CD Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) by imf09.hostedemail.com (Postfix) with ESMTP id 272753000884 for ; Wed, 24 Nov 2021 21:19:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=zK/24Qkt+CUXxwWRIIvMb1Yuxk0SqsiVKxof3LAwFho=; b=FeDgrchxjCm0DOEFAH2BbOpgTw szmGevFWjVGMbpCgxid/aEmkreMVkqLgBu0Pzaqf6Kxg3JAKlRv5VGgFhtvXRz9pEDyfT0VH5dnVs V4RkmYJlIkaXuTcuhB7t3Z0TakccZfNV6JWWMqOofe35Lk9fPH138vuyMgZB43vqfIOFUAAm8HM+/ 8tywOU/SQEXrvmRc60nPvaSqZjquWKqLV+ZP4DOc8P50F25GD9Dr4wikzLxmP5f/Ltr1mmu3FTLrN SL5t2RvjCw1EaKGpd+1LOGqQyra45XXq7koQrBsfncTz/EnYktFdg6B18RQ3QxgDDHh647yDExmK+ neBk2SBQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1mpzft-000JqU-7K; Wed, 24 Nov 2021 21:19:29 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 178D5986843; Wed, 24 Nov 2021 22:19:28 +0100 (CET) Date: Wed, 24 Nov 2021 22:19:27 +0100 From: Peter Zijlstra To: Peter Oskolkov Cc: Ingo Molnar , Thomas Gleixner , Andrew Morton , Dave Hansen , Andy Lutomirski , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Paul Turner , Ben Segall , Peter Oskolkov , Andrei Vagin , Jann Horn , Thierry Delisle Subject: Re: [PATCH v0.9.1 3/6] sched/umcg: implement UMCG syscalls Message-ID: <20211124211927.GG721624@worktop.programming.kicks-ass.net> References: <20211122211327.5931-1-posk@google.com> <20211122211327.5931-4-posk@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211122211327.5931-4-posk@google.com> X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 272753000884 X-Stat-Signature: bsp4cwo73xfzj3x3ofy9chis5g9dnm7y Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=infradead.org header.s=desiato.20200630 header.b=FeDgrchx; spf=none (imf09.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.92.199) smtp.mailfrom=peterz@infradead.org; dmarc=none X-HE-Tag: 1637788772-483430 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: On Mon, Nov 22, 2021 at 01:13:24PM -0800, Peter Oskolkov wrote: > + * Timestamp: a 46-bit CLOCK_MONOTONIC timestamp, at 16ns resolution. > +static int umcg_update_state(u64 __user *state_ts, u64 *expected, u64 desired, > + bool may_fault) > +{ > + u64 curr_ts = (*expected) >> (64 - UMCG_STATE_TIMESTAMP_BITS); > + u64 next_ts = ktime_get_ns() >> UMCG_STATE_TIMESTAMP_GRANULARITY; I'm still very hesitant to use ktime (fear the HPET); but I suppose it makes sense to use a time base that's accessible to userspace. Was MONOTONIC_RAW considered?