AFAIK, stdio buffering - as configurable via setvbuf - is incompatible with PerlIO's buffering, which is why it's disabled when you configure Perl to use PerlIO.  OTOH, you most probably do want PerlIO... so configuring/rebuilding Perl to not use it, isn't really an option.

Anyhow, a little digging around suggests that you can "configure" PerlIO's buffer size in the file perlio.c: 

STDCHAR *
PerlIOBuf_get_base(pTHX_ PerlIO *f)
{
    PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    PERL_UNUSED_CONTEXT;

    if (!b->buf) {
        if (!b->bufsiz)
            b->bufsiz = 4096;   /* <--- here  */
        b->buf = Newxz(b->buf,b->bufsiz, STDCHAR);
        if (!b->buf) {
            b->buf = (STDCHAR *) & b->oneword;
            b->bufsiz = sizeof(b->oneword);
        }
        b->end = b->ptr = b->buf;
    }
    return b->buf;
}

[download]

At least, I changed that 4096 to 8192, recompiled perl (v5.10.0), and now strace reveals that read(2) is being called for blocks of size 8192, when you execute something like 

open my $fh, "<", $^X or die;
while (<$fh>) { }

[download]

while before the change, read blocks were of size 4096.

Other than that, I haven't done any testing yet. So, no guarantees whatsoever (!) that it'll work in every respect... — just something to play with at your own risk.  Good luck!

In reply to Re: 4k read buffer is too small by almut
in thread 4k read buffer is too small by voeckler

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