NetBSD Problem Report #52666

From www@NetBSD.org  Sat Oct 28 18:38:50 2017
Return-Path: <www@NetBSD.org>
Received: from mail.netbsd.org (mail.netbsd.org [199.233.217.200])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(Client CN "mail.NetBSD.org", Issuer "mail.NetBSD.org CA" (not verified))
	by mollari.NetBSD.org (Postfix) with ESMTPS id 7123A7A1DC
	for <gnats-bugs@gnats.NetBSD.org>; Sat, 28 Oct 2017 18:38:50 +0000 (UTC)
Message-Id: <20171028183849.8A5E87A210@mollari.NetBSD.org>
Date: Sat, 28 Oct 2017 18:38:49 +0000 (UTC)
From: coypu@sdf.org
Reply-To: coypu@sdf.org
To: gnats-bugs@NetBSD.org
Subject: ARM spinlocks are suboptimal
X-Send-Pr-Version: www-1.0

>Number:         52666
>Category:       port-arm
>Synopsis:       ARM spinlocks are suboptimal
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-arm-maintainer
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Oct 28 18:40:00 +0000 2017
>Closed-Date:    Sat Dec 09 21:49:54 +0000 2017
>Last-Modified:  Sat Dec 09 21:49:54 +0000 2017
>Originator:     coypu
>Release:        NetBSD 8.99.5
>Organization:
>Environment:
NetBSD 8.99.5
>Description:
newer ARM has an instruction 'wfe' essentially made for spinlocks. we should use it, but I don't see a relevant use of it, only an unused macro.

(In fact only x86 has a spinlock backoff function).
>How-To-Repeat:

>Fix:

>Release-Note:

>Audit-Trail:
From: Matt Thomas <matt@3am-software.com>
To: gnats-bugs@NetBSD.org
Cc: port-arm-maintainer@netbsd.org,
 gnats-admin@netbsd.org,
 netbsd-bugs@netbsd.org
Subject: Re: port-arm/52666: ARM spinlocks are suboptimal
Date: Tue, 31 Oct 2017 16:10:03 -0700

 > On Oct 28, 2017, at 11:40 AM, coypu@SDF.ORG wrote:
 >=20
 >> Number:         52666
 >> Category:       port-arm
 >> Synopsis:       ARM spinlocks are suboptimal
 >> Confidential:   no
 >> Severity:       serious
 >> Priority:       medium
 >> Responsible:    port-arm-maintainer
 >> State:          open
 >> Class:          sw-bug
 >> Submitter-Id:   net
 >> Arrival-Date:   Sat Oct 28 18:40:00 +0000 2017
 >> Originator:     coypu
 >> Release:        NetBSD 8.99.5
 >> Organization:
 >> Environment:
 > NetBSD 8.99.5
 >> Description:
 > newer ARM has an instruction 'wfe' essentially made for spinlocks. we =
 should use it, but I don't see a relevant use of it, only an unused =
 macro.
 >=20
 > (In fact only x86 has a spinlock backoff function).
 >> How-To-Repeat:
 >=20
 >> Fix:
 >=20


 Note that the sev 'send event' instruction needs to be used in parallel. =
  When I experimented earlier I found that wfe/sev would many spurious =
 wakeups negating advantages.=

State-Changed-From-To: open->closed
State-Changed-By: maya@NetBSD.org
State-Changed-When: Sat, 09 Dec 2017 21:49:54 +0000
State-Changed-Why:
Actual benchmark showed otherwise


>Unformatted:

NetBSD Home
NetBSD PR Database Search

(Contact us) $NetBSD: query-full-pr,v 1.39 2013/11/01 18:47:49 spz Exp $
$NetBSD: gnats_config.sh,v 1.8 2006/05/07 09:23:38 tsutsui Exp $
Copyright © 1994-2014 The NetBSD Foundation, Inc. ALL RIGHTS RESERVED.