Re: port-vax/41139: pipe(2) seems broken on VAX

[christos%zoulas.com@localhost (Christos Zoulas)]

The following reply was made to PR port-vax/41139; it has been noted by GNATS.

From: christos%zoulas.com@localhost (Christos Zoulas)
To: gnats-bugs%NetBSD.org@localhost, port-vax-maintainer%netbsd.org@localhost, 
        gnats-admin%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost, 
tsutsui%ceres.dti.ne.jp@localhost
Cc: 
Subject: Re: port-vax/41139: pipe(2) seems broken on VAX
Date: Tue, 7 Apr 2009 17:41:00 -0400

 On Apr 7,  9:25pm, mhitch%lightning.msu.montana.edu@localhost ("Michael L. 
Hitch") wrote:
 -- Subject: Re: port-vax/41139: pipe(2) seems broken on VAX
 
 | The following reply was made to PR port-vax/41139; it has been noted by 
GNATS.
 | 
 | From: "Michael L. Hitch" <mhitch%lightning.msu.montana.edu@localhost>
 | To: gnats-bugs%NetBSD.org@localhost
 | Cc: 
 | Subject: Re: port-vax/41139: pipe(2) seems broken on VAX
 | Date: Tue, 7 Apr 2009 14:48:39 -0600 (MDT)
 | 
 |     The problem appears to only occur when the requested transfer size is > 
 |  PIPE_SIZE, and an additional buffer of BIG_PIPE_SIZE is allocated and 
 |  used.  The defaults are 16KB and 64KB respectively.  Setting BIG_PIPE_SIZE 
 |  to a smaller value (I've tested 63KB) seems to cure the problem.  The real 
 |  root of the problem is that sys_pipe.c uses uiomove() to transfer the 
 |  data, which uses copyin()/copyout().  On the vax, this is done with the 
 |  movc3 instruction, which uses a 16-bit length, and will not transfer 
 |  anything when the length is 0 (which it will be with a 64KB size).
 |  
 |     The simplest fix would be to set BIG_PIPE_SIZE in 
 |  sys/arch/vax/include/param.h.  There does appear to be an improvment 
 |  between using 32KB and 63KB in the one test I did.
 |  
 |     A better fix would be to make copyin()/copyout() work with 64KB or 
 |  larger sizes.  I'm not sure what performance impact that might have 
 |  though.  The quick test I just did shows that just fixing copyin/copyout 
 |  to check for 64KB and transfer one byte with movb before doing the movc3 
 |  seems to show that it was slightly slower than when I was using a 63KB 
 |  BIG_PIPE_SIZE.
 |  
 |     One other note - this also appears to have been the problem with using 
 |  scp on the vax to transfer files.  My scp copies no longer get corrupted 
 |  data.  [Since scp does a pipe to run the remote ssh command and copies the 
 |  data from the pipe, this makes sense.]
 
 
 Can't we do?
 
        while (len >= 64K) {
                movc3 64K-1, ...
                len -= 64K-1;
        }
        movc3 len, ...
 
 In kcopy, copyin and copyout?
 
 christos