[dpdk-dev] [PATCH] hash: update jhash function with the latest available

[De Lara Guarch, Pablo]

> -----Original Message-----
> From: Richardson, Bruce
> Sent: Thursday, April 16, 2015 3:01 PM
> To: De Lara Guarch, Pablo
> Cc: dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] hash: update jhash function with the latest
> available
> 
> On Thu, Apr 16, 2015 at 02:26:59PM +0100, Pablo de Lara wrote:
> > Jenkins hash function was developed originally in 1996,
> > and was integrated in first versions of DPDK.
> > The function has been improved in 2006,
> > achieving up to 60% better performance, compared to the original one.
> >
> > Check out: http://burtleburtle.net/bob/c/lookup3.c
> >
> > This patch integrates that code in the rte_jhash library,
> > adding also a new function rte_jhash_word2,
> > that returns two different hash values, for a single key.
> >
> 
> Should the addition of the new functionality not be a separate patch from
> the
> update to the existing code?

True, actually, I miss one extra function (2 in total).

> Also, do the new functions return the exact same values as the previous
> versions,
> just faster?

The new functions return different values from the previous version
AND faster (some cases, MUCH faster)

[...]

> > +#if RTE_BYTE_ORDER == RTE_LITTLE_ENDIAN
> > +		case 12:
> > +			c += k[2]; b += k[1]; a += k[0]; break;
> > +		case 11:
> > +			c += k[2]&0xffffff; b += k[1]; a += k[0]; break;
> > +		case 10:
> > +			c += k[2]&0xffff; b += k[1]; a += k[0]; break;
> > +		case 9:
> > +			c += k[2]&0xff; b += k[1]; a += k[0]; break;
> > +		case 8:
> > +			b += k[1]; a += k[0]; break;
> > +		case 7:
> > +			b += k[1]&0xffffff; a += k[0]; break;
> > +		case 6:
> > +			b += k[1]&0xffff; a += k[0]; break;
> > +		case 5:
> > +			b += k[1]&0xff; a += k[0]; break;
> > +		case 4:
> > +			a += k[0]; break;
> > +		case 3:
> > +			a += k[0]&0xffffff; break;
> > +		case 2:
> > +			a += k[0]&0xffff; break;
> > +		case 1:
> > +			a += k[0]&0xff; break;
> > +#else
> > +		case 12:
> > +			c += k[2]; b += k[1]; a += k[0]; break;
> > +		case 11:
> > +			c += k[2]&0xffffff00; b += k[1]; a += k[0]; break;
> > +		case 10:
> > +			c += k[2]&0xffff0000; b += k[1]; a += k[0]; break;
> > +		case 9:
> > +			c += k[2]&0xff000000; b += k[1]; a += k[0]; break;
> > +		case 8:
> > +			b += k[1]; a += k[0]; break;
> > +		case 7:
> > +			b += k[1]&0xffffff00; a += k[0]; break;
> > +		case 6:
> > +			b += k[1]&0xffff0000; a += k[0]; break;
> > +		case 5:
> > +			b += k[1]&0xff000000; a += k[0]; break;
> > +		case 4:
> > +			a += k[0]; break;
> > +		case 3:
> > +			a += k[0]&0xffffff00; break;
> > +		case 2:
> > +			a += k[0]&0xffff0000; break;
> > +		case 1:
> > +			a += k[0]&0xff000000; break;
> > +#endif
> 
> Only the constants seem different in this block. Can we get rid of the
> #ifdefs using rte_XX_to_cpu() calls instead?

Will add that in next version.

> 
> > +		/* zero length strings require no mixing */
> > +		case 0:
> > +			return c;
> > +		};
> > +#if RTE_BYTE_ORDER == RTE_LITTLE_ENDIAN
> > +	} else if ((u.i & 0x1) == 0) {
> > +		/* read 16-bit chunks */
> > +		const uint16_t *k = (const uint16_t *)key;
> > +		const uint8_t  *k8;
> > +
> > +		/* all but last block: aligned reads and different mixing */
> > +		while (length > 12) {
> > +			a += k[0] + (((uint32_t)k[1])<<16);
> > +			b += k[2] + (((uint32_t)k[3])<<16);
> > +			c += k[4] + (((uint32_t)k[5])<<16);
> > +
> > +			__rte_jhash_mix(a, b, c);
> > +
> > +			k += 6;
> > +			length -= 12;
> > +		}
> > +
> > +		/* handle the last (probably partial) block */
> > +		k8 = (const uint8_t *)k;
> > +		switch (length) {
> > +		case 12:
> > +			c += k[4]+(((uint32_t)k[5])<<16);
> > +			b += k[2]+(((uint32_t)k[3])<<16);
> > +			a += k[0]+(((uint32_t)k[1])<<16);
> > +			break;
> > +		case 11:
> > +			/* fall through */
> > +			c += ((uint32_t)k8[10])<<16;
> > +		case 10:
> > +			c += k[4];
> > +			b += k[2]+(((uint32_t)k[3])<<16);
> > +			a += k[0]+(((uint32_t)k[1])<<16);
> > +			break;
> > +		case 9:
> > +			/* fall through */
> > +			c += k8[8];
> > +		case 8:
> > +			b += k[2]+(((uint32_t)k[3])<<16);
> > +			a += k[0]+(((uint32_t)k[1])<<16);
> > +			break;
> > +		case 7:
> > +			/* fall through */
> > +			b += ((uint32_t)k8[6])<<16;
> > +		case 6:
> > +			b += k[2];
> > +			a += k[0]+(((uint32_t)k[1])<<16);
> > +			break;
> > +		case 5:
> > +			/* fall through */
> > +			b += k8[4];
> > +		case 4:
> > +			a += k[0]+(((uint32_t)k[1])<<16);
> > +			break;
> > +		case 3:
> > +			/* fall through */
> > +			a += ((uint32_t)k8[2])<<16;
> > +		case 2:
> > +			a += k[0];
> > +			break;
> > +		case 1:
> > +			a += k8[0];
> > +			break;
> > +		case 0:
> > +			/* zero length requires no mixing */
> > +			return c;
> > +		}
> > +#endif
> 
> No else block for this ifdef?

According to the code, for big endian, it only covers 4-byte alignment and rest of cases.

> 
> > +	} else {
> > +		const uint8_t *k = (const uint8_t *)key;
> > +
> > +		/* all but the last block: affect some 32 bits of (a, b, c) */
> > +		while (length > 12) {
> > +#if RTE_BYTE_ORDER == RTE_LITTLE_ENDIAN
> > +			a += k[0];
> > +			a += ((uint32_t)k[1])<<8;
> > +			a += ((uint32_t)k[2])<<16;
> > +			a += ((uint32_t)k[3])<<24;
> > +			b += k[4];
> > +			b += ((uint32_t)k[5])<<8;
> > +			b += ((uint32_t)k[6])<<16;
> > +			b += ((uint32_t)k[7])<<24;
> > +			c += k[8];
> > +			c += ((uint32_t)k[9])<<8;
> > +			c += ((uint32_t)k[10])<<16;
> > +			c += ((uint32_t)k[11])<<24;
> > +#else
> > +			a += ((uint32_t)k[0])<<24;
> > +			a += ((uint32_t)k[1])<<16;
> > +			a += ((uint32_t)k[2])<<8;
> > +			a += ((uint32_t)k[3]);
> > +			b += ((uint32_t)k[4])<<24;
> > +			b += ((uint32_t)k[5])<<16;
> > +			b += ((uint32_t)k[6])<<8;
> > +			b += ((uint32_t)k[7]);
> > +			c += ((uint32_t)k[8])<<32;
> > +			c += ((uint32_t)k[9])<<16;
> > +			c += ((uint32_t)k[10])<<8;
> > +			c += ((uint32_t)k[11]);
> > +#endif
> 
> Maybe find a better way to shorten/remove this #ifdef also. E.g. shorter
> ifdef defining macros for the different shift amounts, 0, 8, 16, 24.

Agree. Will change that in v2.

[...]

Thanks for the comments. I will send a v2 soon.