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From: Theodore.Papadopoulo@sophia.inria.fr To: gcc-gnats@gcc.gnu.org Subject: libstdc++/2211: Performance regression for cin.read with respect to g++-2.95.2 ? Date: Sun, 01 Apr 2001 00:00:00 -0000 [thread overview] Message-ID: <20010307191657.8381.qmail@sourceware.cygnus.com> (raw) >Number: 2211 >Category: libstdc++ >Synopsis: Performance regression for cin.read with respect to g++-2.95.2 ? >Confidential: no >Severity: non-critical >Priority: medium >Responsible: unassigned >State: open >Class: sw-bug >Submitter-Id: net >Arrival-Date: Wed Mar 07 11:26:01 PST 2001 >Closed-Date: >Last-Modified: >Originator: Theo Papadopoulo >Release: unknown-1.0 >Organization: >Environment: g++ mainline from 01/22/2001 Linus redhat 6.2 on x86 (P III) >Description: I have a huge performance problem with a call to a libstdc++-v3 function. istream::read. This is true only for I/O done with cin. mururoa->ls -l toto -rw-r--r-- 1 papadop robotvis 1367160 Mar 7 11:38 toto mururoa->cat toto toto | ./a.out ~/Robotvis++/Libs/Image/tests/images/scully.float.inr Before ifstream::read: 983970673 After ifstream::read: 983970673 Before cin.read: 983970673 After cin.read: 983970682 Before fread: 983970682 After fread: 983970682 With g++-2.95.2, I get: mururoa->/usr/local/bin/g++ -g -pg -ftemplate-depth-30 -fPIC -DPIC Test.C mururoa->cat toto toto | ./a.out ~/Robotvis++/Libs/Image/tests/images/scully.float.inr Before ifstream::read: 983978303 After ifstream::read: 983978303 Before cin.read: 983978303 After cin.read: 983978303 Before fread: 983978303 After fread: 983978303 [regression 2.95.2 was cin.read(ing) as that as the other ways of reading] The crux of the problem seem to be (in fstream.tcc). // XXX So that istream::getc() will only need to get 1 char, // as opposed to BUF_SIZE. if (__fd == 0) _M_buf_size = 1; Consequently, characters are read one by one which is extremely costly. >How-To-Repeat: >Fix: >Release-Note: >Audit-Trail: >Unformatted: ----gnatsweb-attachment---- Content-Type: application/octet-stream; name="Test.C" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="Test.C" I2luY2x1ZGUgPGlvc3RyZWFtPgojaW5jbHVkZSA8ZnN0cmVhbT4KI2luY2x1ZGUgPHN0ZGlvLmg+ CiNpbmNsdWRlIDx0aW1lLmg+CgppbnQKbWFpbihpbnQgYXJnYyxjaGFyICphcmd2W10pCnsKICAg IGNvbnN0IHVuc2lnbmVkIGRhdGFfc2l6ZSA9IDEzNjcxNjA7CiAgICBjaGFyIGRhdGFbZGF0YV9z aXplXTsKCiAgICBzdGQ6Omlmc3RyZWFtIGlmcyhhcmd2WzFdKTsKCiAgICBzdGQ6OmNlcnIgPDwg IkJlZm9yZSBpZnN0cmVhbTo6cmVhZDogIiA8PCB0aW1lKDApIDw8IHN0ZDo6ZW5kbDsKICAgIGlm cy5yZWFkKGRhdGEsZGF0YV9zaXplKTsKICAgIHN0ZDo6Y2VyciA8PCAiQWZ0ZXIgaWZzdHJlYW06 OnJlYWQ6ICIgPDwgdGltZSgwKSA8PCBzdGQ6OmVuZGw7CgogICAgc3RkOjpjZXJyIDw8ICJCZWZv cmUgY2luLnJlYWQ6ICIgPDwgdGltZSgwKSA8PCBzdGQ6OmVuZGw7CiAgICBzdGQ6OmNpbi5yZWFk KGRhdGEsZGF0YV9zaXplKTsKICAgIHN0ZDo6Y2VyciA8PCAiQWZ0ZXIgY2luLnJlYWQ6ICIgPDwg dGltZSgwKSA8PCBzdGQ6OmVuZGw7CgogICAgc3RkOjpjZXJyIDw8ICJCZWZvcmUgZnJlYWQ6ICIg PDwgdGltZSgwKSA8PCBzdGQ6OmVuZGw7CiAgICBmcmVhZChkYXRhLDEsZGF0YV9zaXplLHN0ZGlu KTsKICAgIHN0ZDo6Y2VyciA8PCAiQWZ0ZXIgZnJlYWQ6ICIgPDwgdGltZSgwKSA8PCBzdGQ6OmVu ZGw7Cn0K
next reply other threads:[~2001-04-01 0:00 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2001-04-01 0:00 Theodore.Papadopoulo [this message] 2001-06-26 17:19 bkoz 2002-01-27 15:27 rodrigc
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