Re: [PATCH 11/11] kvm tools: Modify term_putc to write more than one char

Andreas Herrmann
2014-05-12T11:21:11Z

On Wed, May 07, 2014 at 07:58:30PM +0400, Sergei Shtylyov wrote:
> Hello.
>
> On 06-05-2014 19:51, Andreas Herrmann wrote:
>
> >From: David Daney <david.daney@cavium.com>
>
> >It is a performance enhancement. When running in a simulator, each
> >system call to write a character takes a lot of time. Batching them
> >up decreases the overhead (in the root kernel) of each virtio console
> >write.
>
> >Signed-off-by: David Daney <david.daney@cavium.com>
> >Signed-off-by: Andreas Herrmann <andreas.herrmann@caviumnetworks.com>
> >---
> > tools/kvm/term.c | 7 +++++--
> > 1 file changed, 5 insertions(+), 2 deletions(-)
>
> >diff --git a/tools/kvm/term.c b/tools/kvm/term.c
> >index 3de410b..b153eed 100644
> >--- a/tools/kvm/term.c
> >+++ b/tools/kvm/term.c
> >@@ -52,11 +52,14 @@ int term_getc(struct kvm *kvm, int term)
> > int term_putc(char *addr, int cnt, int term)
> > {
> > int ret;
> >+ int num_remaining = cnt;
> >
> >- while (cnt--) {
> >- ret = write(term_fds[term][TERM_FD_OUT], addr++, 1);
> >+ while (num_remaining) {
> >+ ret = write(term_fds[term][TERM_FD_OUT], addr, num_remaining);
> > if (ret < 0)
> > return 0;
>
> Perhaps 'return cnt - num_remaining' instead?

Although all current callers of this function are not checking the
return value I aggree that this change would be nice to have.

I wouldn't make this change within this patch though.
(I'll add a separate patch to modify the return value.)

> >+ num_remaining -= ret;
> >+ addr += ret;
> > }
> >
> > return cnt;
>
> WBR, Sergei

Thanks,
Andreas