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Revision d0313e629f2690edfd269896b398048275227db0 authored by Ian Rogers on 12 August 2022, 23:09:49 UTC, committed by Arnaldo Carvalho de Melo on 13 August 2022, 18:03:09 UTC 
perf jevents: Fold strings optimization
 
If a shorter string ends a longer string then the shorter string may
reuse the longer string at an offset. For example, on x86 the event
arith.cycles_div_busy and cycles_div_busy can be folded, even though
they have difference names the strings are identical after 6
characters. cycles_div_busy can reuse the arith.cycles_div_busy string
at an offset of 6.

In pmu-events.c this looks like the following where the 'also:' lists
folded strings:

/* offset=177541 */ "arith.cycles_div_busy\000\000pipeline\000Cycles the divider is busy\000\000\000event=0x14,period=2000000,umask=0x1\000\000\000\000\000\000\000\000\000" /* also: cycles_div_busy\000\000pipeline\000Cycles the divider is busy\000\000\000event=0x14,period=2000000,umask=0x1\000\000\000\000\000\000\000\000\000 */

As jevents.py combines multiple strings for an event into a larger
string, the amount of folding is minimal as all parts of the event must
align. Other organizations can benefit more from folding, but lose space
by say recording more offsets.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.garry@huawei.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Will Deacon <will@kernel.org>
Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com>
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20220812230949.683239-15-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
1 parent 9118259
Raw File
crc32_generic.c 
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright 2012 Xyratex Technology Limited
 */

/*
 * This is crypto api shash wrappers to crc32_le.
 */

#include <asm/unaligned.h>
#include <linux/crc32.h>
#include <crypto/internal/hash.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/string.h>
#include <linux/kernel.h>

#define CHKSUM_BLOCK_SIZE	1
#define CHKSUM_DIGEST_SIZE	4

/** No default init with ~0 */
static int crc32_cra_init(struct crypto_tfm *tfm)
{
	u32 *key = crypto_tfm_ctx(tfm);

	*key = 0;

	return 0;
}

/*
 * Setting the seed allows arbitrary accumulators and flexible XOR policy
 * If your algorithm starts with ~0, then XOR with ~0 before you set
 * the seed.
 */
static int crc32_setkey(struct crypto_shash *hash, const u8 *key,
			unsigned int keylen)
{
	u32 *mctx = crypto_shash_ctx(hash);

	if (keylen != sizeof(u32))
		return -EINVAL;
	*mctx = get_unaligned_le32(key);
	return 0;
}

static int crc32_init(struct shash_desc *desc)
{
	u32 *mctx = crypto_shash_ctx(desc->tfm);
	u32 *crcp = shash_desc_ctx(desc);

	*crcp = *mctx;

	return 0;
}

static int crc32_update(struct shash_desc *desc, const u8 *data,
			unsigned int len)
{
	u32 *crcp = shash_desc_ctx(desc);

	*crcp = crc32_le(*crcp, data, len);
	return 0;
}

/* No final XOR 0xFFFFFFFF, like crc32_le */
static int __crc32_finup(u32 *crcp, const u8 *data, unsigned int len,
			 u8 *out)
{
	put_unaligned_le32(crc32_le(*crcp, data, len), out);
	return 0;
}

static int crc32_finup(struct shash_desc *desc, const u8 *data,
		       unsigned int len, u8 *out)
{
	return __crc32_finup(shash_desc_ctx(desc), data, len, out);
}

static int crc32_final(struct shash_desc *desc, u8 *out)
{
	u32 *crcp = shash_desc_ctx(desc);

	put_unaligned_le32(*crcp, out);
	return 0;
}

static int crc32_digest(struct shash_desc *desc, const u8 *data,
			unsigned int len, u8 *out)
{
	return __crc32_finup(crypto_shash_ctx(desc->tfm), data, len,
			     out);
}
static struct shash_alg alg = {
	.setkey		= crc32_setkey,
	.init		= crc32_init,
	.update		= crc32_update,
	.final		= crc32_final,
	.finup		= crc32_finup,
	.digest		= crc32_digest,
	.descsize	= sizeof(u32),
	.digestsize	= CHKSUM_DIGEST_SIZE,
	.base		= {
		.cra_name		= "crc32",
		.cra_driver_name	= "crc32-generic",
		.cra_priority		= 100,
		.cra_flags		= CRYPTO_ALG_OPTIONAL_KEY,
		.cra_blocksize		= CHKSUM_BLOCK_SIZE,
		.cra_ctxsize		= sizeof(u32),
		.cra_module		= THIS_MODULE,
		.cra_init		= crc32_cra_init,
	}
};

static int __init crc32_mod_init(void)
{
	return crypto_register_shash(&alg);
}

static void __exit crc32_mod_fini(void)
{
	crypto_unregister_shash(&alg);
}

subsys_initcall(crc32_mod_init);
module_exit(crc32_mod_fini);

MODULE_AUTHOR("Alexander Boyko <alexander_boyko@xyratex.com>");
MODULE_DESCRIPTION("CRC32 calculations wrapper for lib/crc32");
MODULE_LICENSE("GPL");
MODULE_ALIAS_CRYPTO("crc32");
MODULE_ALIAS_CRYPTO("crc32-generic");
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