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

Andreas Herrmann
2014-05-06T15:51:31Z

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;
+ num_remaining -= ret;
+ addr += ret;
}

return cnt;
--
1.7.9.5