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 X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 51BD7ECDE5F for ; Thu, 19 Jul 2018 15:08:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 00AB720862 for ; Thu, 19 Jul 2018 15:08:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="cm5gGTFb" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 00AB720862 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731917AbeGSPwI (ORCPT ); Thu, 19 Jul 2018 11:52:08 -0400 Received: from mail-io0-f196.google.com ([209.85.223.196]:38249 "EHLO mail-io0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731567AbeGSPwI (ORCPT ); Thu, 19 Jul 2018 11:52:08 -0400 Received: by mail-io0-f196.google.com with SMTP id v26-v6so7343423iog.5; Thu, 19 Jul 2018 08:08:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=k9XyS2+Bjfxgi4gGbi43c33wHKsoxIM0ST7EsX47Tuw=; b=cm5gGTFbP0qWGa010xXAjOG7WIcdtNXFTliB3RbeVdpfkaCwQPGf5oOrlhtA5OKL1n Za4Zxs4GzVrgvVJCTyYM+uxaN9LuROjHZ7MwRcm/RgaZ39EyrhqLqoSMnnoR9WZ4dAnn agoCsLjIFsyZy4xfZngAIaHd6zO4o4EoJqiRQ= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=k9XyS2+Bjfxgi4gGbi43c33wHKsoxIM0ST7EsX47Tuw=; b=M8pBoWCtt7iQX5AKl3JZv2OYN26MJjU6o6NWBm6nB8XzEgI+85R6EG8yFT1xJOZbbr nJWsXpMfuOfRW/qRgGlcUh1HodTThGkZ8WmUC0zfGJhvFqHQlBiVgFHBwlK0ogt+MjF8 Eqhh4xZGsagGV/VWKWSsgUPmMJKjaxsPAzzUl7Ks/GHXdzfhYmTCQ0BNyvINgyeuoRiT X24gNs09O/fM92qapWocDme/C1L3Vq0Z2Dt0ZrNHxg+IyAOfDcdLXtgAgLuuivMCY8+Y 3NWD1rgV/8fpoHbYmwB+80BS055ntKlslU5YoYHujnPHIGtdXSYHqA1c6Ud5WxXeL1mY fjBQ== X-Gm-Message-State: AOUpUlH7j7byWTD8cL2mTy4PIoiznR9r8fPw9SrN/9SUEchP9gbJLFb7 BqDNes3Towk2VgjuIB9FPdclPvIMzray3RrsaZw= X-Google-Smtp-Source: AAOMgpchUxS0q/FR3EYMnuS7ERDVbtREJFPkmhFa3Png8gRPxVUKp/2AuSyD5m8j2qxz9UGXAWW2eKPIDoDcMs0HOr8= X-Received: by 2002:a6b:f612:: with SMTP id n18-v6mr1663888ioh.259.1532012911924; Thu, 19 Jul 2018 08:08:31 -0700 (PDT) MIME-Version: 1.0 References: <20180712172942.10094-1-hannes@cmpxchg.org> <20180712172942.10094-9-hannes@cmpxchg.org> <20180718120318.GC2476@hirez.programming.kicks-ass.net> In-Reply-To: <20180718120318.GC2476@hirez.programming.kicks-ass.net> From: Linus Torvalds Date: Thu, 19 Jul 2018 08:08:20 -0700 Message-ID: Subject: Re: [PATCH 08/10] psi: pressure stall information for CPU, memory, and IO To: Peter Zijlstra Cc: Johannes Weiner , Ingo Molnar , Andrew Morton , Tejun Heo , surenb@google.com, Vinayak Menon , Christoph Lameter , Mike Galbraith , shakeelb@google.com, linux-mm , cgroups , Linux Kernel Mailing List , kernel-team Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 18, 2018 at 5:03 AM Peter Zijlstra wrote: > > And as said before, we can compress the state from 12 bytes, to 6 bits > (or 1 byte), giving another 11 bytes for 59 bytes free. > > Leaving us just 5 bytes short of needing a single cacheline :/ Do you actually need 64 bits for the times? That's the big cost. And it seems ridiculous, if you actually care about size. You already have a 64-bit start time. Everything else is some cumulative relative time. Do those really need 64-bit and nanosecond resolution? Maybe a 32-bit microsecond would be ok - would you ever account more than 35 minutes of anything without starting anew? Linus