Messages in this thread | | | Date | Mon, 6 Aug 2012 09:19:10 -0400 | From | Cyril Chemparathy <> | Subject | Re: [PATCH 01/22] ARM: add mechanism for late code patching |
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On 8/6/2012 7:12 AM, Russell King - ARM Linux wrote: > On Tue, Jul 31, 2012 at 07:04:37PM -0400, Cyril Chemparathy wrote: >> +static void __init init_patch_kernel(void) >> +{ >> + const void *start = &__patch_table_begin; >> + const void *end = &__patch_table_end; >> + >> + BUG_ON(patch_kernel(start, end - start)); >> + flush_icache_range(init_mm.start_code, init_mm.end_code); > > Err. You are asking the kernel to flush every single cache line > manually throughout the kernel code. That's a flush every 32-bytes > over maybe a few megabytes of address space. >
With a flush_cache_all(), we could avoid having to operate a cacheline at a time, but that clobbers way more than necessary.
Maybe the better answer is to flush only the patched cachelines.
> This is one of the reasons we do the patching in assembly code before > the caches are enabled - so we don't have to worry about the interaction > with the CPU caches, which for this kind of application would be very > expensive. >
Sure, flushing caches is expensive. But then, so is running the patching code with caches disabled. I guess memory access latencies drive the performance trade off here.
-- Thanks - Cyril
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