From: Stefan Hajnoczi <stefanha@redhat.com>
To: qemu-devel@nongnu.org
Cc: Peter Maydell <peter.maydell@linaro.org>,
Stefan Hajnoczi <stefanha@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>
Subject: [Qemu-devel] [PULL 1/3] iov: avoid memcpy for "simple" iov_from_buf/iov_to_buf
Date: Tue, 9 Feb 2016 15:11:29 +0000 [thread overview]
Message-ID: <1455030691-18489-2-git-send-email-stefanha@redhat.com> (raw)
In-Reply-To: <1455030691-18489-1-git-send-email-stefanha@redhat.com>
From: Paolo Bonzini <pbonzini@redhat.com>
memcpy can take a large amount of time for small reads and writes.
For virtio it is a common case that the first iovec can satisfy the
whole read or write. In that case, and if bytes is a constant to
avoid excessive growth of code, inline the first iteration
into the caller.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1450782213-14227-1-git-send-email-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
include/qemu/iov.h | 34 ++++++++++++++++++++++++++++++----
util/iov.c | 8 ++++----
2 files changed, 34 insertions(+), 8 deletions(-)
diff --git a/include/qemu/iov.h b/include/qemu/iov.h
index 569b2c2..2847551 100644
--- a/include/qemu/iov.h
+++ b/include/qemu/iov.h
@@ -39,10 +39,36 @@ size_t iov_size(const struct iovec *iov, const unsigned int iov_cnt);
* such "large" value is -1 (sinice size_t is unsigned),
* so specifying `-1' as `bytes' means 'up to the end of iovec'.
*/
-size_t iov_from_buf(const struct iovec *iov, unsigned int iov_cnt,
- size_t offset, const void *buf, size_t bytes);
-size_t iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt,
- size_t offset, void *buf, size_t bytes);
+size_t iov_from_buf_full(const struct iovec *iov, unsigned int iov_cnt,
+ size_t offset, const void *buf, size_t bytes);
+size_t iov_to_buf_full(const struct iovec *iov, const unsigned int iov_cnt,
+ size_t offset, void *buf, size_t bytes);
+
+static inline size_t
+iov_from_buf(const struct iovec *iov, unsigned int iov_cnt,
+ size_t offset, const void *buf, size_t bytes)
+{
+ if (__builtin_constant_p(bytes) && iov_cnt &&
+ offset <= iov[0].iov_len && bytes <= iov[0].iov_len - offset) {
+ memcpy(iov[0].iov_base + offset, buf, bytes);
+ return bytes;
+ } else {
+ return iov_from_buf_full(iov, iov_cnt, offset, buf, bytes);
+ }
+}
+
+static inline size_t
+iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt,
+ size_t offset, void *buf, size_t bytes)
+{
+ if (__builtin_constant_p(bytes) && iov_cnt &&
+ offset <= iov[0].iov_len && bytes <= iov[0].iov_len - offset) {
+ memcpy(buf, iov[0].iov_base + offset, bytes);
+ return bytes;
+ } else {
+ return iov_to_buf_full(iov, iov_cnt, offset, buf, bytes);
+ }
+}
/**
* Set data bytes pointed out by iovec `iov' of size `iov_cnt' elements,
diff --git a/util/iov.c b/util/iov.c
index e802ee1..062f4e5 100644
--- a/util/iov.c
+++ b/util/iov.c
@@ -20,8 +20,8 @@
#include "qemu/iov.h"
#include "qemu/sockets.h"
-size_t iov_from_buf(const struct iovec *iov, unsigned int iov_cnt,
- size_t offset, const void *buf, size_t bytes)
+size_t iov_from_buf_full(const struct iovec *iov, unsigned int iov_cnt,
+ size_t offset, const void *buf, size_t bytes)
{
size_t done;
unsigned int i;
@@ -39,8 +39,8 @@ size_t iov_from_buf(const struct iovec *iov, unsigned int iov_cnt,
return done;
}
-size_t iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt,
- size_t offset, void *buf, size_t bytes)
+size_t iov_to_buf_full(const struct iovec *iov, const unsigned int iov_cnt,
+ size_t offset, void *buf, size_t bytes)
{
size_t done;
unsigned int i;
--
2.5.0
next prev parent reply other threads:[~2016-02-09 15:40 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-09 15:11 [Qemu-devel] [PULL 0/3] Block patches Stefan Hajnoczi
2016-02-09 15:11 ` Stefan Hajnoczi [this message]
2016-02-09 15:11 ` [Qemu-devel] [PULL 2/3] blockjob: Fix hang in block_job_finish_sync Stefan Hajnoczi
2016-02-09 15:11 ` [Qemu-devel] [PULL 3/3] block: add missing call to bdrv_drain_recurse Stefan Hajnoczi
2016-02-09 19:34 ` [Qemu-devel] [PULL 0/3] Block patches Peter Maydell
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