Commit 6d25a633 authored by Nick Terrell's avatar Nick Terrell Committed by Ingo Molnar
Browse files

lib: Prepare zstd for preboot environment, improve performance 

These changes are necessary to get the build to work in the preboot
environment, and to get reasonable performance:

- Remove a double definition of the CHECK_F macro when the zstd
  library is amalgamated.

- Switch ZSTD_copy8() to __builtin_memcpy(), because in the preboot
  environment on x86 gcc can't inline `memcpy()` otherwise.

- Limit the gcc hack in ZSTD_wildcopy() to the broken gcc version. See
  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81388

.

ZSTD_copy8() and ZSTD_wildcopy() are in the core of the zstd hot loop.
So outlining these calls to memcpy(), and having an extra branch are very
detrimental to performance.

Signed-off-by: default avatarNick Terrell <terrelln@fb.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Tested-by: default avatarSedat Dilek <sedat.dilek@gmail.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200730190841.2071656-2-nickrterrell@gmail.com
parent 92ed3019

lib/zstd/fse_decompress.c

+1 −8
Original line number Diff line number Diff line
@@ -47,6 +47,7 @@ 
****************************************************************/

#include "bitstream.h"

#include "fse.h"

#include "zstd_internal.h"

#include <linux/compiler.h>

#include <linux/kernel.h>

#include <linux/string.h> /* memcpy, memset */
@@ -60,14 +61,6 @@ 
		enum { FSE_static_assert = 1 / (int)(!!(c)) }; \

	} /* use only *after* variable declarations */



/* check and forward error code */

#define CHECK_F(f)                  \

	{                           \

		size_t const e = f; \

		if (FSE_isError(e)) \

			return e;   \

	}



/* **************************************************************

*  Templates

****************************************************************/

lib/zstd/zstd_internal.h

+12 −2
Original line number Diff line number Diff line
@@ -127,7 +127,14 @@ static const U32 OF_defaultNormLog = OF_DEFAULTNORMLOG; 
*  Shared functions to include for inlining

*********************************************/

ZSTD_STATIC void ZSTD_copy8(void *dst, const void *src) {

	memcpy(dst, src, 8);

	/*

	 * zstd relies heavily on gcc being able to analyze and inline this

	 * memcpy() call, since it is called in a tight loop. Preboot mode

	 * is compiled in freestanding mode, which stops gcc from analyzing

	 * memcpy(). Use __builtin_memcpy() to tell gcc to analyze this as a

	 * regular memcpy().

	 */

	__builtin_memcpy(dst, src, 8);

}

/*! ZSTD_wildcopy() :

*   custom version of memcpy(), can copy up to 7 bytes too many (8 bytes if length==0) */
@@ -137,13 +144,16 @@ ZSTD_STATIC void ZSTD_wildcopy(void *dst, const void *src, ptrdiff_t length) 
	const BYTE* ip = (const BYTE*)src;

	BYTE* op = (BYTE*)dst;

	BYTE* const oend = op + length;

	/* Work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81388.

#if defined(GCC_VERSION) && GCC_VERSION >= 70000 && GCC_VERSION < 70200

	/*

	 * Work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81388.

	 * Avoid the bad case where the loop only runs once by handling the

	 * special case separately. This doesn't trigger the bug because it

	 * doesn't involve pointer/integer overflow.

	 */

	if (length <= 8)

		return ZSTD_copy8(dst, src);

#endif

	do {

		ZSTD_copy8(op, ip);

		op += 8;

CRA Git | Maintained and supported by SUSTech CRA and CCSE