[Tcl-bugs] [Bug #119148] IO_PERFORMANCE on NT 80 times slower then on unix

[<no...@so...>]

Bug #119148, was updated on 2000-Oct-25 22:02
Here is a current snapshot of the bug.

Project: Tcl
Category: Channel Types
Status: Open
Resolution: None
Bug Group: 8.0.3
Priority: 6
Submitted by: nobody
Assigned to : nobody
Summary: IO_PERFORMANCE on NT 80 times slower then on unix

Details: OriginalBugID: 948 Bug
Version: 8.0.3
SubmitDate: '1998-12-14'
LastModified: '2000-06-22'
Severity: MED
Status: Assigned
Submitter: pat
ChangedBy: hobbs
OS: Windows NT
Machine: X86
FixedDate: '2000-10-25'
ClosedDate: '2000-10-25'


Name: Uwe Traum

ReproducibleScript:

proc dotest {{filename test.bin}} {
    set fid [open $filename w]
    fconfigure $fid -translation binary

    for { set i 0 } { $i < 2000 } { incr i } {
        set ind [expr {128*int(rand()*30000)}]
        #seek $fid $ind start
        puts -nonewline $fid "123456789012345678901234567890"
    }
    close $fid
}
time dotest 3

[rewritten by hobbs as proc]

ObservedBehavior:
Output:

NT4;local disk;PentiumPro 200: 155172000 microseconds per iteration
Solaris2.5;local disk;sparc20: 1844860 microseconds per iteration

on unix it's 80 time faster than on NT!!!

DesiredBehavior:
same speed


In FileOutputProc (tcl8.0.3/win/tclWinChan.c,line 560) there
is ALWAYS a call to FlushFileBuffers. 
So every I/O is written directly to disk. 
That's why the Disk-LED is permanently blinking.

What's the reason for this call ?
Can it be removed ?

thanks 
--
This is verified in 8.4a1.  The disk LED does stay permanently
on under NT.  Using the Performance Monitor, it does seem that
excessive flushing may be occuring.
 
-- 06/22/2000 hobbs

Follow-Ups:

Date: 2001-Jan-31 12:45
By: dkf

Comment:
See also Bug #119300 - we've so many unclosed bugs that it is impractical
to link related ones... <sigh>)
-------------------------------------------------------

Date: 2001-Jan-12 16:35
By: davygrvy

Comment:
File channel driver on Win* forces a flush.  It really doesn't need to, but
some file tests depend on it doing a true write to disk.  So therefore,
it's slower.
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For detailed info, follow this link:
http://sourceforge.net/bugs/?func=detailbug&bug_id=119148&group_id=10894