Re: [PATCH v2 1/5] [ppc] Process dynamic relocations for kernel

On Fri, 2011-11-04 at 14:06 +0530, Suzuki Poulose wrote:

On 11/03/11 05:06, Josh Poimboeuf wrote:

quoted

On Tue, 2011-10-25 at 17:23 +0530, Suzuki K. Poulose wrote:

@@ -137,6 +137,9 @@ get_type:
  	lwz	r0, 8(r9)	/* r_addend */
  	add	r0, r0, r3	/* final addend */
  	stwx	r0, r4, r7	/* memory[r4+r7]) = (u32)r0 */
+	dcbst	r4,r7		/* flush dcache line to memory */
+	sync			/* wait for flush to complete */
+	icbi	r4,r7		/* invalidate icache line */

Doing it this way has two drawbacks :

1) Placing it here in relocate would do the flushing for each and every update.

I agree.  My kernel had around 80,000 relocations, which means 80,000
d-cache line flushes (for a 32k d-cache) and 80,000 i-cache line
invalidates (for a 32k i-cache).  Which is obviously a little overkill.
Although I didn't notice a performance hit during boot.

2) I would like to keep this code as generic as possible for the PPC32 code.

Could we move this to the place from relocate is called and flush the d-cache and
i-cache entirely ?

Why not put the cache flushing code at the end of relocate?  Would some
of the other PPC32 platforms not require the cache flushing?

My PPC32 knowledge is 4xx-centric, so please feel free to rewrite the
patch as needed to accommodate other PPC32 cores.


Thanks,
Josh