Re: [PATCH 2/3] lib: zlib_inflate: improves decompression performance
On Wed, Nov 11, 2020 at 5:06 PM Zhaoxiu Zeng wrote:
> 在 2020/11/11 11:46, Jann Horn 写道:
> > On Mon, Nov 9, 2020 at 8:27 PM wrote:
> >> This patch does:
> >> 1. Cleanup code and reduce branches
> >> 2. Use copy_from_back to copy the matched bytes from the back output buffer
> >
> > What exactly is copy_from_back()? Is it like memmove()? If yes, have
> > you tried using memmove() instead of the code added in patch 1/3?
> >
>
> If use memcpy(or memmove), the code will be like this:
> while (dist < len) {
> memcpy(out, out - dist, dist);
> out += dist;
> len -= dist;
> }
> memcpy(out, out - dist, len);
Ah, thanks. So basically it means: "repeatedly copy a pattern of
length `dist` from `out-dist` to `out` until `len` bytes have been
written"
Re: [PATCH 2/3] lib: zlib_inflate: improves decompression performance
在 2020/11/11 11:46, Jann Horn 写道:
> On Mon, Nov 9, 2020 at 8:27 PM wrote:
>> This patch does:
>> 1. Cleanup code and reduce branches
>> 2. Use copy_from_back to copy the matched bytes from the back output buffer
>
> What exactly is copy_from_back()? Is it like memmove()? If yes, have
> you tried using memmove() instead of the code added in patch 1/3?
>
If use memcpy(or memmove), the code will be like this:
while (dist < len) {
memcpy(out, out - dist, dist);
out += dist;
len -= dist;
}
memcpy(out, out - dist, len);
or:
const u8 * const from = out - dist;
while (dist < len) {
memcpy(out, from, dist);
out += dist;
len -= dist;
dist *= 2;
}
memcpy(out, from, len);
In addition, the len is small in most cases, so the function calls are
expensive.
Re: [PATCH 2/3] lib: zlib_inflate: improves decompression performance
On Mon, Nov 9, 2020 at 8:27 PM wrote: > This patch does: > 1. Cleanup code and reduce branches > 2. Use copy_from_back to copy the matched bytes from the back output buffer What exactly is copy_from_back()? Is it like memmove()? If yes, have you tried using memmove() instead of the code added in patch 1/3?
[PATCH 2/3] lib: zlib_inflate: improves decompression performance
From: Zhaoxiu Zeng
This patch does:
1. Cleanup code and reduce branches
2. Use copy_from_back to copy the matched bytes from the back output buffer
I tested on 5.8.18-300.fc33.x86_64.
The performance of function zlib_inflate is improved by about 7%.
If the CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS is disabled in copy_from_back.h,
the performance is improved by about 5%.
Signed-off-by: Zhaoxiu Zeng
---
lib/zlib_inflate/inffast.c | 122 ++---
1 file changed, 17 insertions(+), 105 deletions(-)
diff --git a/lib/zlib_inflate/inffast.c b/lib/zlib_inflate/inffast.c
index ed1f3df27260..c27e45fc5335 100644
--- a/lib/zlib_inflate/inffast.c
+++ b/lib/zlib_inflate/inffast.c
@@ -4,29 +4,13 @@
*/
#include
+#include
#include "inftrees.h"
#include "inflate.h"
#include "inffast.h"
#ifndef ASMINF
-union uu {
- unsigned short us;
- unsigned char b[2];
-};
-
-/* Endian independed version */
-static inline unsigned short
-get_unaligned16(const unsigned short *p)
-{
- union uu mm;
- unsigned char *b = (unsigned char *)p;
-
- mm.b[0] = b[0];
- mm.b[1] = b[1];
- return mm.us;
-}
-
/*
Decode literal, length, and distance codes and write out the resulting
literal and match bytes until either not enough input or output is
@@ -184,104 +168,32 @@ void inflate_fast(z_streamp strm, unsigned start)
state->mode = BAD;
break;
}
-from = window;
-if (write == 0) { /* very common case */
-from += wsize - op;
-if (op < len) { /* some from window */
-len -= op;
-do {
-*out++ = *from++;
-} while (--op);
-from = out - dist; /* rest from output */
-}
-}
-else if (write < op) { /* wrap around window */
-from += wsize + write - op;
-op -= write;
-if (op < len) { /* some from end of window */
-len -= op;
-do {
-*out++ = *from++;
-} while (--op);
-from = window;
-if (write < len) { /* some from start of window */
-op = write;
+from = window + write - op;
+if (write < op) { /* very common case */
+from += wsize;
+if (write) {/* wrap around window */
+op -= write;
+if (op < len) { /* some from end of window */
len -= op;
do {
*out++ = *from++;
} while (--op);
-from = out - dist; /* rest from output */
+from = window; /* some from start of window */
+op = write;
}
}
}
-else { /* contiguous in window */
-from += write - op;
-if (op < len) { /* some from window */
-len -= op;
-do {
-*out++ = *from++;
-} while (--op);
-from = out - dist; /* rest from output */
-}
-}
-while (len > 2) {
-*out++ = *from++;
-*out++ = *from++;
-*out++ = *from++;
-len -= 3;
-}
-if (len) {
-*out++ = *from++;
-if (len > 1)
+if (op < len) { /* some from window */
+len -= op; /* rest from output */
+do {
*out++ = *from++;
+} while (--op);
+} else {
+dist = out - from;
}
}
-else {
- unsigned short *sout;
- unsigned long loops;
-
-from = out - dist; /* copy direct from output */
- /* minimum length is three */
- /* Align out addr */
- if (!((long)(out - 1) & 1)) {
- *out++ = *from++;
-
