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=-3.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 9568AC31E45 for ; Thu, 13 Jun 2019 16:12:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C04420679 for ; Thu, 13 Jun 2019 16:12:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="DuXyWXqH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391626AbfFMQMN (ORCPT ); Thu, 13 Jun 2019 12:12:13 -0400 Received: from mail-io1-f67.google.com ([209.85.166.67]:43051 "EHLO mail-io1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731223AbfFMQMK (ORCPT ); Thu, 13 Jun 2019 12:12:10 -0400 Received: by mail-io1-f67.google.com with SMTP id k20so18143373ios.10 for ; Thu, 13 Jun 2019 09:12:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=6v/23h74yo3j/zUughy0wFFC9yfO7oR+qGcuy0DJBZk=; b=DuXyWXqHXbK8HuFNvok5v3l44KGSaXUZ1sTcFqSZMnKszMlUEbzqFaaqQKvrgWdt46 YYkGsl/GqHupyJpXzDqjbJB5SvCmaNd07MaC3gtGS19OoCkNrhvVaEi1/Fyj0w5IwK10 NYvTsRGyh722FTs2L1AN0LF1/jyu/pNUmRZsU= 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:content-transfer-encoding; bh=6v/23h74yo3j/zUughy0wFFC9yfO7oR+qGcuy0DJBZk=; b=dCtYgCVlT8ky252gKgYoh7H3wyf3vbG0YA+LApifCsmIs7xhF35j9Jd8HNGhjQqXGl ncSvFxiAWCflKBH/7QhhDIQX4ZFiCOSg6gLso3LV0D+oB1Xuew4K7f/rp1LEaWajLhfi IYfKQO0drovSqOEp+/WwU5YMQWlymwz23D+83id2CBicJ0M02eCDorNLselih6SjTSqQ tzYWYxwe4jsvWjAcHNSAt2HuoS6EsAivU9Y38soSpzqOWoWll+zgawjeSbYIUB/m+CAJ aXpKt+w+OPFcmSZojrL0fHDCdDWOMch37o22tCuECibPKhOS7MXLOS+l/nS69uzuWZ4f GF8Q== X-Gm-Message-State: APjAAAVxcmWxu6+iUH/PmgnJqAlXSGNFwTM9k8SYFtslMtukA8HRNBAj I0E+m+n/InrprFHOQminfv8nc3WgsbI= X-Google-Smtp-Source: APXvYqyXg0pDc+TvjpEgv1yZrMXS6g+2xKTjSDahD0IMW0IM3A7LIg+f0J0HLX08p0YXKKjN/9Jckg== X-Received: by 2002:a02:a806:: with SMTP id f6mr61450916jaj.74.1560442329423; Thu, 13 Jun 2019 09:12:09 -0700 (PDT) Received: from mail-io1-f49.google.com (mail-io1-f49.google.com. [209.85.166.49]) by smtp.gmail.com with ESMTPSA id t133sm502930iof.21.2019.06.13.09.12.08 for (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Thu, 13 Jun 2019 09:12:08 -0700 (PDT) Received: by mail-io1-f49.google.com with SMTP id u13so18174364iop.0 for ; Thu, 13 Jun 2019 09:12:08 -0700 (PDT) X-Received: by 2002:a5e:db0a:: with SMTP id q10mr11718339iop.168.1560442328298; Thu, 13 Jun 2019 09:12:08 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Doug Anderson Date: Thu, 13 Jun 2019 09:11:56 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v1] iopoll: Tweak readx_poll_timeout sleep range To: Marc Gonzalez Cc: Arnd Bergmann , Will Deacon , Linux ARM , LKML , Thierry Reding , Andrew Morton , Bjorn Andersson , Thomas Gleixner , Bjorn Helgaas Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Thu, Jun 13, 2019 at 9:04 AM Marc Gonzalez wro= te: > > On 13/06/2019 14:42, Arnd Bergmann wrote: > > > On Thu, Jun 13, 2019 at 2:16 PM Marc Gonzalez wrote: > > > >> Chopping max delay in 4 seems excessive. Let's just cut it in half. > >> > >> Signed-off-by: Marc Gonzalez > >> --- > >> When max_us=3D100, old_min was 26 us; new_min would be 50 us > >> Was there a good reason for the 1/4th? > >> Is new_min=3D0 a problem? (for max=3D1) > > > > You normally want a large enough range between min and max. I don't > > see anything wrong with a factor of four. > > Hmmm, I expect the typical use-case to be: > "HW manual states operation X completes in 100 =C2=B5s. > Let's call usleep_range(100, foo); before hitting the reg." > > And foo needs to be a "reasonable" value: big enough to be able > to merge several requests, low enough not to wait too long after > the HW is ready. > > In this case, I'd say usleep_range(100, 200); makes sense. > > Come to think of it, I'm not sure min=3D26 (or min=3D50) makes sense... > Why wait *less* than what the user specified? IIRC usleep_range() nearly always tries to sleep for the max. My recollection of the design is that you only end up with something less than the max if the system was going to wake up anyway. In such a case it seems like it wouldn't be insane to go and check if the condition is already true if 25% of the time has passed. Maybe you'll get lucky and you can return early. Are you actually seeing problems with the / 4, or is this patch just a result of code inspection? -Doug 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=-3.7 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,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 0C2C1C31E45 for ; Thu, 13 Jun 2019 16:12:17 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id D54F320679 for ; Thu, 13 Jun 2019 16:12:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="GLDT7UHO"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="DuXyWXqH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D54F320679 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chromium.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:To:Subject:Message-ID:Date:From: In-Reply-To:References:MIME-Version:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=fKbAaMJiQD+8Apeg+Fmi7xfZzBHhP9tBG8VUQww/j2I=; b=GLDT7UHOY5RTCI h0F6H6V1rMA1BRYpxxyJVhcIRWh4vYJ9b1gfx6KhrS1+zqNojCbyHyJHGh6+Sn7AmC4ZC16JSR2B3 HuXmhz/NT6e+SQNPHui+fbEJxXIzsjbZ/R6bCQyJjjJ2iE01v1hiDLW0i9Eou0aTNPr8kzXtWpTS2 qd6kqlqiFuZF57P9V5jSYORmi5TgOfWO6TgwAUf1tE8wthOP6DEkHyj7eCVxb3PtsKAuV7ALOisbg ri7bBfh6welMutqbhVezDfiKE/3cx2YInX0/iqOPY5eSj7GVvsLDk6cvk1HeglWx9a6lH+DZWWTi1 lcj2O9f/vmYcQwdSIH8Q==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hbSKl-00007x-HI; Thu, 13 Jun 2019 16:12:15 +0000 Received: from mail-io1-xd43.google.com ([2607:f8b0:4864:20::d43]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1hbSKi-00007N-FA for linux-arm-kernel@lists.infradead.org; Thu, 13 Jun 2019 16:12:13 +0000 Received: by mail-io1-xd43.google.com with SMTP id n5so18144545ioc.7 for ; Thu, 13 Jun 2019 09:12:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=6v/23h74yo3j/zUughy0wFFC9yfO7oR+qGcuy0DJBZk=; b=DuXyWXqHXbK8HuFNvok5v3l44KGSaXUZ1sTcFqSZMnKszMlUEbzqFaaqQKvrgWdt46 YYkGsl/GqHupyJpXzDqjbJB5SvCmaNd07MaC3gtGS19OoCkNrhvVaEi1/Fyj0w5IwK10 NYvTsRGyh722FTs2L1AN0LF1/jyu/pNUmRZsU= 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:content-transfer-encoding; bh=6v/23h74yo3j/zUughy0wFFC9yfO7oR+qGcuy0DJBZk=; b=UR1cx2LpZgE6lZKCY5/s1IxUVjX/SjxjzQzO41zPVS7aFm1cucjtRbWy6ooEcfE8MI UbTCfNxJa2GijkEa2LlrKABHcAJ6aOyd2oNBi81XwiwxiXu4zJdJNMpJ5F3SDsXjW8VU 88tLtjpOY0A7K7KAJWtrQ+syeslw26tmp70g0foKQzkDzM/+v8IcH0FXzOUMamA1tBPM bCiD8XSbFllg/vRpiCKVXXxeZPKNSivmnzBL1u/k+U/OQQYZxfu6cBpOJwwEqZX+AKa6 Qu2iPVNxidZki/57FoiL7kqIxRMqvVmRY8h7zafJEpodGlP1Wwt/8QCUoQdJw5mYa7T4 jXdg== X-Gm-Message-State: APjAAAVv13tU+63qOTPvC27LWOIowQDsLtYE9ZsZ9kAs5Ar/NDg3Hdcq R8wNWlnIMwk8BoyHhYjDU9I3ezFUZqY= X-Google-Smtp-Source: APXvYqyUYVd2Rhq6+5bvk5xH7rq8XQuStxDs9Q57lBa+TVgcTdN8/zX45+j2kiNmgMsIjdjP+tWx+A== X-Received: by 2002:a5d:9ec4:: with SMTP id a4mr791895ioe.125.1560442331255; Thu, 13 Jun 2019 09:12:11 -0700 (PDT) Received: from mail-io1-f52.google.com (mail-io1-f52.google.com. [209.85.166.52]) by smtp.gmail.com with ESMTPSA id o7sm346943ioo.81.2019.06.13.09.12.08 for (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Thu, 13 Jun 2019 09:12:09 -0700 (PDT) Received: by mail-io1-f52.google.com with SMTP id k13so18154613iop.5 for ; Thu, 13 Jun 2019 09:12:08 -0700 (PDT) X-Received: by 2002:a5e:db0a:: with SMTP id q10mr11718339iop.168.1560442328298; Thu, 13 Jun 2019 09:12:08 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Doug Anderson Date: Thu, 13 Jun 2019 09:11:56 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v1] iopoll: Tweak readx_poll_timeout sleep range To: Marc Gonzalez X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190613_091212_534936_344D9113 X-CRM114-Status: GOOD ( 18.34 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Arnd Bergmann , Will Deacon , LKML , Bjorn Andersson , Thierry Reding , Bjorn Helgaas , Andrew Morton , Thomas Gleixner , Linux ARM Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org SGksCgpPbiBUaHUsIEp1biAxMywgMjAxOSBhdCA5OjA0IEFNIE1hcmMgR29uemFsZXogPG1hcmMu dy5nb256YWxlekBmcmVlLmZyPiB3cm90ZToKPgo+IE9uIDEzLzA2LzIwMTkgMTQ6NDIsIEFybmQg QmVyZ21hbm4gd3JvdGU6Cj4KPiA+IE9uIFRodSwgSnVuIDEzLCAyMDE5IGF0IDI6MTYgUE0gTWFy YyBHb256YWxleiB3cm90ZToKPiA+Cj4gPj4gQ2hvcHBpbmcgbWF4IGRlbGF5IGluIDQgc2VlbXMg ZXhjZXNzaXZlLiBMZXQncyBqdXN0IGN1dCBpdCBpbiBoYWxmLgo+ID4+Cj4gPj4gU2lnbmVkLW9m Zi1ieTogTWFyYyBHb256YWxleiA8bWFyYy53LmdvbnphbGV6QGZyZWUuZnI+Cj4gPj4gLS0tCj4g Pj4gV2hlbiBtYXhfdXM9MTAwLCBvbGRfbWluIHdhcyAyNiB1czsgbmV3X21pbiB3b3VsZCBiZSA1 MCB1cwo+ID4+IFdhcyB0aGVyZSBhIGdvb2QgcmVhc29uIGZvciB0aGUgMS80dGg/Cj4gPj4gSXMg bmV3X21pbj0wIGEgcHJvYmxlbT8gKGZvciBtYXg9MSkKPiA+Cj4gPiBZb3Ugbm9ybWFsbHkgd2Fu dCBhIGxhcmdlIGVub3VnaCByYW5nZSBiZXR3ZWVuIG1pbiBhbmQgbWF4LiBJIGRvbid0Cj4gPiBz ZWUgYW55dGhpbmcgd3Jvbmcgd2l0aCBhIGZhY3RvciBvZiBmb3VyLgo+Cj4gSG1tbSwgSSBleHBl Y3QgdGhlIHR5cGljYWwgdXNlLWNhc2UgdG8gYmU6Cj4gIkhXIG1hbnVhbCBzdGF0ZXMgb3BlcmF0 aW9uIFggY29tcGxldGVzIGluIDEwMCDCtXMuCj4gTGV0J3MgY2FsbCB1c2xlZXBfcmFuZ2UoMTAw LCBmb28pOyBiZWZvcmUgaGl0dGluZyB0aGUgcmVnLiIKPgo+IEFuZCBmb28gbmVlZHMgdG8gYmUg YSAicmVhc29uYWJsZSIgdmFsdWU6IGJpZyBlbm91Z2ggdG8gYmUgYWJsZQo+IHRvIG1lcmdlIHNl dmVyYWwgcmVxdWVzdHMsIGxvdyBlbm91Z2ggbm90IHRvIHdhaXQgdG9vIGxvbmcgYWZ0ZXIKPiB0 aGUgSFcgaXMgcmVhZHkuCj4KPiBJbiB0aGlzIGNhc2UsIEknZCBzYXkgdXNsZWVwX3JhbmdlKDEw MCwgMjAwKTsgbWFrZXMgc2Vuc2UuCj4KPiBDb21lIHRvIHRoaW5rIG9mIGl0LCBJJ20gbm90IHN1 cmUgbWluPTI2IChvciBtaW49NTApIG1ha2VzIHNlbnNlLi4uCj4gV2h5IHdhaXQgKmxlc3MqIHRo YW4gd2hhdCB0aGUgdXNlciBzcGVjaWZpZWQ/CgpJSVJDIHVzbGVlcF9yYW5nZSgpIG5lYXJseSBh bHdheXMgdHJpZXMgdG8gc2xlZXAgZm9yIHRoZSBtYXguICBNeQpyZWNvbGxlY3Rpb24gb2YgdGhl IGRlc2lnbiBpcyB0aGF0IHlvdSBvbmx5IGVuZCB1cCB3aXRoIHNvbWV0aGluZyBsZXNzCnRoYW4g dGhlIG1heCBpZiB0aGUgc3lzdGVtIHdhcyBnb2luZyB0byB3YWtlIHVwIGFueXdheS4gIEluIHN1 Y2ggYQpjYXNlIGl0IHNlZW1zIGxpa2UgaXQgd291bGRuJ3QgYmUgaW5zYW5lIHRvIGdvIGFuZCBj aGVjayBpZiB0aGUKY29uZGl0aW9uIGlzIGFscmVhZHkgdHJ1ZSBpZiAyNSUgb2YgdGhlIHRpbWUg aGFzIHBhc3NlZC4gIE1heWJlIHlvdSdsbApnZXQgbHVja3kgYW5kIHlvdSBjYW4gcmV0dXJuIGVh cmx5LgoKQXJlIHlvdSBhY3R1YWxseSBzZWVpbmcgcHJvYmxlbXMgd2l0aCB0aGUgLyA0LCBvciBp cyB0aGlzIHBhdGNoIGp1c3QgYQpyZXN1bHQgb2YgY29kZSBpbnNwZWN0aW9uPwoKLURvdWcKCl9f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fCmxpbnV4LWFybS1r ZXJuZWwgbWFpbGluZyBsaXN0CmxpbnV4LWFybS1rZXJuZWxAbGlzdHMuaW5mcmFkZWFkLm9yZwpo dHRwOi8vbGlzdHMuaW5mcmFkZWFkLm9yZy9tYWlsbWFuL2xpc3RpbmZvL2xpbnV4LWFybS1rZXJu ZWwK