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

Sergei Shtylyov
2014-05-07T15:58:16Z

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?

> + num_remaining -= ret;
> + addr += ret;
> }
>
> return cnt;

WBR, Sergei