Re: [9/9] powerpc: optimise csum_partial() call when len is constant
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From: Scott Wood <oss@buserror.net>
Date: 2016-03-05 05:29:14
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On Tue, Sep 22, 2015 at 04:34:36PM +0200, Christophe Leroy wrote:
quoted hunk ↗ jump to hunk
+/* + * computes the checksum of a memory block at buff, length len, + * and adds in "sum" (32-bit) + * + * returns a 32-bit number suitable for feeding into itself + * or csum_tcpudp_magic + * + * this function must be called with even lengths, except + * for the last fragment, which may be odd + * + * it's best to have buff aligned on a 32-bit boundary + */ +__wsum __csum_partial(const void *buff, int len, __wsum sum); + +static inline __wsum csum_partial(const void *buff, int len, __wsum sum) +{ + if (__builtin_constant_p(len) && len == 0) + return sum; + + if (__builtin_constant_p(len) && len <= 16 && (len & 1) == 0) { + __wsum sum1; + + if (len == 2) + sum1 = (__force u32)*(u16 *)buff; + if (len >= 4) + sum1 = *(u32 *)buff; + if (len == 6) + sum1 = csum_add(sum1, (__force u32)*(u16 *)(buff + 4)); + if (len >= 8) + sum1 = csum_add(sum1, *(u32 *)(buff + 4)); + if (len == 10) + sum1 = csum_add(sum1, (__force u32)*(u16 *)(buff + 8)); + if (len >= 12) + sum1 = csum_add(sum1, *(u32 *)(buff + 8)); + if (len == 14) + sum1 = csum_add(sum1, (__force u32)*(u16 *)(buff + 12)); + if (len >= 16) + sum1 = csum_add(sum1, *(u32 *)(buff + 12)); + + sum = csum_add(sum1, sum);
Why the final csum_add instead of s/sum1/sum/ and putting csum_add in the "len == 2" and "len >= 4" cases? The (__force u32) casts are unnecessary. Or rather, it should be (__force __wsum) -- on all of them, not just the 16-bit ones. The pointer casts should be const.
+ } else if (__builtin_constant_p(len) && (len & 3) == 0) {
+ sum = csum_add(ip_fast_csum_nofold(buff, len >> 2), sum);It may not make a functional difference, but based on the csum_add() argument names and other csum_add() usage, sum should come first and the new content second. -Scott