Re: [PATCH 2/5] kvx: Implement dcache invalidation primitive

[Jules Maselbas <jmaselbas@kalray.eu>]

On Tue, Mar 02, 2021 at 09:40:50AM +0100, Ahmad Fatoum wrote:
> Hello,
> 
> > +
> > +void kvx_dcache_invalidate_mem_area(uint64_t addr, int size)
> > +{
> > +	/* if hwloop iterations cost < _K1_DCACHE_REFILL_PERCENT cache refill,
> > +	 * use hwloop, otherwise invalid the whole cache
> > +	 */
> > +	if (size <
> > +	(K1_DCACHE_REFILL_PERCENT * (K1_DCACHE_REFILL * K1_DCACHE_SIZE))
> > +			/ (100 * (K1_DCACHE_REFILL + K1_DCACHE_HWLOOP))) {
> > +		/* number of lines that must be invalidated */
> > +		int invalid_lines = ((addr + size) -
> > +					(addr & (~(K1_DCACHE_LINE_SIZE - 1))));
> > +
> > +		invalid_lines = invalid_lines / K1_DCACHE_LINE_SIZE
> > +				+ (0 != (invalid_lines % K1_DCACHE_LINE_SIZE));
> > +		if (__builtin_constant_p(invalid_lines) && invalid_lines <= 2) {
> 
> Note that currently this will always be false, because of lack of link time
> optimization. You could split this away the check into the header and leave the
> juicy parts here if you want to have this optimization.
> 
Yes we can drop one branch, I am tempted to always invalidate the whole
cache and be done with it. I will send a new patch anyway.

> > +			/* when inlining (and doing constant folding),
> > +			 *  gcc is able to unroll small loops
> > +			 */
> > +			int i;
> > +
> > +			for (i = 0; i < invalid_lines; i++) {
> > +				__builtin_kvx_dinvall((void *)(addr
> > +						+ i * K1_DCACHE_LINE_SIZE));
> > +			}
> > +		} else if (invalid_lines > 0) {
> > +			__asm__ __volatile__ (
> > +				"loopdo %1, 0f\n;;\n"
> > +				"dinvall 0[%0]\n"
> > +				"addd %0 = %0, %2\n;;\n"
> > +				"0:\n"
> > +				: "+r"(addr)
> > +				: "r" (invalid_lines),
> > +				"i" (K1_DCACHE_LINE_SIZE)
> > +				: "ls", "le", "lc", "memory");
> > +		}
> > +	} else {
> > +		__builtin_kvx_dinval();
> > +	}
> > +}
> > 
> 
> -- 
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