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author | Paolo Bonzini <pbonzini@redhat.com> | 2015-12-22 12:03:33 +0100 |
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committer | Stefan Hajnoczi <stefanha@redhat.com> | 2016-02-09 13:52:26 +0000 |
commit | ad523bca56a7202d2498c550a41be5c986c4d33c (patch) | |
tree | b3b07fcce95eefd07483b22923de1c4ae62b10bb | |
parent | ee8e8f92a730afc17ab8be6e86df6b9a23b8ebc6 (diff) | |
download | qemu-ad523bca56a7202d2498c550a41be5c986c4d33c.zip qemu-ad523bca56a7202d2498c550a41be5c986c4d33c.tar.gz qemu-ad523bca56a7202d2498c550a41be5c986c4d33c.tar.bz2 |
iov: avoid memcpy for "simple" iov_from_buf/iov_to_buf
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>
-rw-r--r-- | include/qemu/iov.h | 34 | ||||
-rw-r--r-- | 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, @@ -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; |