X-Recipient:	archive-cygwin AT delorie DOT com
DomainKey-Signature:	a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id
	:list-unsubscribe:list-subscribe:list-archive:list-post
	:list-help:sender:from:subject:reply-to:to:references:message-id
	:date:mime-version:in-reply-to:content-type
	:content-transfer-encoding; q=dns; s=default; b=s9nZpevvbWXnLq0U
	Wf0wZmz/yVK9A0oHNyY9RjeCVbGUKRjtJbyUxfrokzQEWkulSre+JYxo6VnmZpwv
	B7z8+iZEkyWTeDdwq3W8uaRB531cHtBPMhnEpqRC9KhD9CRxveWx6GwGfLpHgSfV
	vVEPlZsBx6reUfG7pGu3y0H5hYA=
DKIM-Signature:	v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id
	:list-unsubscribe:list-subscribe:list-archive:list-post
	:list-help:sender:from:subject:reply-to:to:references:message-id
	:date:mime-version:in-reply-to:content-type
	:content-transfer-encoding; s=default; bh=zImCBcvfJ9mq/7cQaxdSfp
	2t6iQ=; b=ac/jhImWsjaXURantvEAAsl1mvtsKCH2HeWdYfzgo1kyNJq5uHYx66
	PJlujYu/IP5IrzAmdOmU5jzIvUr+a6NPKBxFHum4W5TcH6eoNYtpz5kt/SE8/l+N
	5o8BjeJ+BMyD4MLaRlaSPnDkkDJcs3HdgZWPh0oWM9kkzWTpuGM4o=
Mailing-List:	contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Id:	<cygwin.cygwin.com>
List-Subscribe:	<mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive:	<http://sourceware.org/ml/cygwin/>
List-Post:	<mailto:cygwin AT cygwin DOT com>
List-Help:	<mailto:cygwin-help AT cygwin DOT com>, <http://sourceware.org/ml/#faqs>
Sender:	cygwin-owner AT cygwin DOT com
Mail-Followup-To:	cygwin AT cygwin DOT com
Delivered-To:	mailing list cygwin AT cygwin DOT com
Authentication-Results:	sourceware.org; auth=none
X-Spam-SWARE-Status:	No, score=-3.2 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_LOW autolearn=ham version=3.3.1 spammy=Norman, norman, 1809, pst
X-HELO:	smtp-out-so.shaw.ca
From:	Brian Inglis <Brian DOT Inglis AT SystematicSw DOT ab DOT ca>
Subject:	Re: thread_local performance using g++ for cygwin
Reply-To:	Brian DOT Inglis AT SystematicSw DOT ab DOT ca
To:	cygwin AT cygwin DOT com
References:	<alpine DOT WNT DOT 2 DOT 00 DOT 1905052026250 DOT 14000 AT panamint>
Openpgp:	preference=signencrypt
Message-ID:	<36b16ae1-fc0c-a598-480a-ffedad690a76@SystematicSw.ab.ca>
Date:	Mon, 6 May 2019 14:10:31 -0600
User-Agent:	Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1
MIME-Version:	1.0
In-Reply-To:	<alpine.WNT.2.00.1905052026250.14000@panamint>
X-IsSubscribed:	yes

On 2019-05-06 01:09, Arthur Norman wrote:
> The attached code tried two loops each of which just calls a function that
> increments an integer variable. One loop is a simple variable, the other has the
> thread_local qualifier. I put in ugly annotations to prevent g++ from inlining
> the functions even though I compile with -O3, but in real cases separate
> compilation forces each TL access to be independent.
> The timing as between the two cases is EXTREME on cygwin (both 32 and 64-bit)
> however g++ on Linux and the Microsoft compiler on Windows both manage to keep
> the base of thread-local regions in a segment register in such a way that the
> thread_local overhead is minimal. The cygwin thread_local overhead is large
> enough to be very visible in my code as a whole. I can see that changing to use
> a segment register might be a painful API change even if it was feasible, but
> has there been any consideration of it?
> Note that x86_64-w64-mingw32-g++ and clang also do not use the segment register
> so suffer the significant speed penalty, so maybe it would be hard to match what
> Microsoft manage?
> 
> Sample output:
>     simple 1.265
>     thread_local 33.219

See:
https://cygwin.com/git/gitweb.cgi?p=newlib-cygwin.git;f=winsup/cygwin/how-cygtls-works.txt;a=blob

and you may want to compare the gcc default options and -S assembler output for
your test case on Linux and Cygwin, and perhaps also any glibc and newlib TLS
support functions called: running your Linux tests under some WSL distro will
even out OS kernel differences.

My own tests on Win 10.0.17763.437 1809 are worse than yours:

$ g++ -O3 -o tltime.{bin,cpp}
$ ./tltime.bin
simple 1.60938
thread_local 1.95312
$ uname -srvmo
Linux 4.4.0-17763-Microsoft #379-Microsoft Wed Mar 06 19:16:00 PST 2019 x86_64
GNU/Linux
$ head /etc/os-release
PRETTY_NAME="Debian GNU/Linux 9 (stretch)"
NAME="Debian GNU/Linux"
VERSION_ID="9"
VERSION="9 (stretch)"
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"

$ g++ -O3 -o tltime.{exe,cpp}
$ ./tltime.exe
simple 1.608
thread_local 53.25
$ uname -srvmo
CYGWIN_NT-10.0 3.0.7(0.338/5/3) 2019-04-30 18:08 x86_64 Cygwin
$ head /etc/os-release
PRETTY_NAME="Cygwin 64 3.0.7 2019-04-30"
NAME=Cygwin
ID=cygwin
ID_LIKE=msys mingw
VARIANT="64"
VARIANT_ID="x86_64"
VERSION="3.0.7 (0.338/5/3) 2019-04-30 18:08"
VERSION_ID="3.0.7"
BUILD_ID="0.338/5/3 2019-04-30 18:08"
CPE_NAME="cpe:/a:cygwin:cygwin:3.0.7::~~~~x64~Windows%3e%3d6.0"

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

This email may be disturbing to some readers as it contains
too much technical detail. Reader discretion is advised.

--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple

- Raw text -