From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <zsh-workers-return-29172-mason-zsh=primenet.com.au@zsh.org>
Received: (qmail 2825 invoked by alias); 7 May 2011 17:07:01 -0000
Mailing-List: contact zsh-workers-help@zsh.org; run by ezmlm
Precedence: bulk
X-No-Archive: yes
List-Id: Zsh Workers List <zsh-workers.zsh.org>
List-Post: <mailto:zsh-workers@zsh.org>
List-Help: <mailto:zsh-workers-help@zsh.org>
X-Seq: 29172
Received: (qmail 14608 invoked from network); 7 May 2011 17:06:47 -0000
X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on f.primenet.com.au
X-Spam-Level: 
X-Spam-Status: No, score=-2.7 required=5.0 tests=BAYES_00,DKIM_SIGNED,
	DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FROM,RCVD_IN_DNSWL_LOW autolearn=ham
	version=3.3.1
Received-SPF: pass (ns1.primenet.com.au: SPF record at _spf.google.com designates 209.85.220.171 as permitted sender)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=gmail.com; s=gamma;
        h=domainkey-signature:mime-version:date:message-id:subject:from:to
         :content-type;
        bh=gJUZStPKIrh93QyiA/IR2e8GJ7Kc5wcWKYFMbGq1sdY=;
        b=OYSUBV7SfwVdVoW1k1ofQD1gWtFoZ2zvY4cf14eyli/hA2yAPb9m8o6RQ21gnZAKDj
         ssldMo+c1VkNip5APtE9m0BvCV2EndIEv2GfMAS9lGL8C71S+okshnvelRxqks9Wrgll
         /VIuMxazEK1kvoVALuPCWj4vARWAb11x856Ng=
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=mime-version:date:message-id:subject:from:to:content-type;
        b=UfoTFfiqpV7OhYBly8fbApqIwK1fYOJg7brW7uoU6mIOXC45qdWOYMAEjV8hLSSb4q
         j49M05XYu4sbqzoGCkgTLNvs/37OAouCQInF0li4VS9zcDnDMOl4FlXtSAMtLIIRTuSU
         N0wE+ljX2/d+rre9VbFB3Tq9BD62cWFJfLh3I=
MIME-Version: 1.0
Date: Sat, 7 May 2011 19:00:17 +0200
Message-ID: <BANLkTinRzKaUNfzA0K3SsfnvWoU1o+UVDg@mail.gmail.com>
Subject: the source of slow large for loops
From: Mikael Magnusson <mikachu@gmail.com>
To: zsh workers <zsh-workers@zsh.org>
Content-Type: text/plain; charset=UTF-8

I don't know if anyone looked into why things like
for i in {1..700000}; do true; done
is extremely slow in zsh, so I did now. Turns out zhalloc is extremely
slow, and for the above loop, one particular line runs 12049901132
times according to gcov. (It takes around 10 minutes). If I add early
returns of malloc() and realloc() to zhalloc and hrealloc, the loop
runs in 3 seconds (but leaks a couple of hundred megabytes memory).

This is mostly a FYI thing, not really intending to do anything about
it or expecting anything, but I've always wondered where the slowness
was and now I know. :)

-- 
Mikael Magnusson