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Revision 4f988f152ee087831ea5c1c77cda4454cacc052c authored by Linus Torvalds on 04 May 2012, 22:13:54 UTC, committed by Linus Torvalds on 04 May 2012, 22:13:54 UTC 
seqlock: add 'raw_seqcount_begin()' function
 
The normal read_seqcount_begin() function will wait for any current
writers to exit their critical region by looping until the sequence
count is even.

That "wait for sequence count to stabilize" is the right thing to do if
the read-locker will just retry the whole operation on contention: no
point in doing a potentially expensive reader sequence if we know at the
beginning that we'll just end up re-doing it all.

HOWEVER.  Some users don't actually retry the operation, but instead
will abort and do the operation with proper locking.  So the sequence
count case may be the optimistic quick case, but in the presense of
writers you may want to do full locking in order to guarantee forward
progress.  The prime example of this would be the RCU name lookup.

And in that case, you may well be better off without the "retry early",
and are in a rush to instead get to the failure handling.  Thus this
"raw" interface that just returns the sequence number without testing it
- it just forces the low bit to zero so that read_seqcount_retry() will
always fail such a "active concurrent writer" scenario.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent 2f62427
Raw File
tcrypt.h 
/*
 * Quick & dirty crypto testing module.
 *
 * This will only exist until we have a better testing mechanism
 * (e.g. a char device).
 *
 * Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
 * Copyright (c) 2002 Jean-Francois Dive <jef@linuxbe.org>
 * Copyright (c) 2007 Nokia Siemens Networks
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 */
#ifndef _CRYPTO_TCRYPT_H
#define _CRYPTO_TCRYPT_H

struct cipher_speed_template {
	const char *key;
	unsigned int klen;
};

struct hash_speed {
	unsigned int blen;	/* buffer length */
	unsigned int plen;	/* per-update length */
	unsigned int klen;	/* key length */
};

/*
 * DES test vectors.
 */
#define DES3_SPEED_VECTORS	1

static struct cipher_speed_template des3_speed_template[] = {
	{
		.key	= "\x01\x23\x45\x67\x89\xab\xcd\xef"
			  "\x55\x55\x55\x55\x55\x55\x55\x55"
			  "\xfe\xdc\xba\x98\x76\x54\x32\x10",
		.klen	= 24,
	}
};

/*
 * Cipher speed tests
 */
static u8 speed_template_8[] = {8, 0};
static u8 speed_template_24[] = {24, 0};
static u8 speed_template_8_32[] = {8, 32, 0};
static u8 speed_template_16_32[] = {16, 32, 0};
static u8 speed_template_16_24_32[] = {16, 24, 32, 0};
static u8 speed_template_32_40_48[] = {32, 40, 48, 0};
static u8 speed_template_32_48[] = {32, 48, 0};
static u8 speed_template_32_48_64[] = {32, 48, 64, 0};
static u8 speed_template_32_64[] = {32, 64, 0};

/*
 * Digest speed tests
 */
static struct hash_speed generic_hash_speed_template[] = {
	{ .blen = 16,	.plen = 16, },
	{ .blen = 64,	.plen = 16, },
	{ .blen = 64,	.plen = 64, },
	{ .blen = 256,	.plen = 16, },
	{ .blen = 256,	.plen = 64, },
	{ .blen = 256,	.plen = 256, },
	{ .blen = 1024,	.plen = 16, },
	{ .blen = 1024,	.plen = 256, },
	{ .blen = 1024,	.plen = 1024, },
	{ .blen = 2048,	.plen = 16, },
	{ .blen = 2048,	.plen = 256, },
	{ .blen = 2048,	.plen = 1024, },
	{ .blen = 2048,	.plen = 2048, },
	{ .blen = 4096,	.plen = 16, },
	{ .blen = 4096,	.plen = 256, },
	{ .blen = 4096,	.plen = 1024, },
	{ .blen = 4096,	.plen = 4096, },
	{ .blen = 8192,	.plen = 16, },
	{ .blen = 8192,	.plen = 256, },
	{ .blen = 8192,	.plen = 1024, },
	{ .blen = 8192,	.plen = 4096, },
	{ .blen = 8192,	.plen = 8192, },

	/* End marker */
	{  .blen = 0,	.plen = 0, }
};

static struct hash_speed hash_speed_template_16[] = {
	{ .blen = 16,	.plen = 16,	.klen = 16, },
	{ .blen = 64,	.plen = 16,	.klen = 16, },
	{ .blen = 64,	.plen = 64,	.klen = 16, },
	{ .blen = 256,	.plen = 16,	.klen = 16, },
	{ .blen = 256,	.plen = 64,	.klen = 16, },
	{ .blen = 256,	.plen = 256,	.klen = 16, },
	{ .blen = 1024,	.plen = 16,	.klen = 16, },
	{ .blen = 1024,	.plen = 256,	.klen = 16, },
	{ .blen = 1024,	.plen = 1024,	.klen = 16, },
	{ .blen = 2048,	.plen = 16,	.klen = 16, },
	{ .blen = 2048,	.plen = 256,	.klen = 16, },
	{ .blen = 2048,	.plen = 1024,	.klen = 16, },
	{ .blen = 2048,	.plen = 2048,	.klen = 16, },
	{ .blen = 4096,	.plen = 16,	.klen = 16, },
	{ .blen = 4096,	.plen = 256,	.klen = 16, },
	{ .blen = 4096,	.plen = 1024,	.klen = 16, },
	{ .blen = 4096,	.plen = 4096,	.klen = 16, },
	{ .blen = 8192,	.plen = 16,	.klen = 16, },
	{ .blen = 8192,	.plen = 256,	.klen = 16, },
	{ .blen = 8192,	.plen = 1024,	.klen = 16, },
	{ .blen = 8192,	.plen = 4096,	.klen = 16, },
	{ .blen = 8192,	.plen = 8192,	.klen = 16, },

	/* End marker */
	{  .blen = 0,	.plen = 0,	.klen = 0, }
};

#endif	/* _CRYPTO_TCRYPT_H */
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