On 15.10.2018 23:11, James Bottomley wrote: > On Sun, 2018-10-14 at 20:34 +0200, Helge Deller wrote: >> This patch adds the necessary code to patch a running SMP kernel >> at runtime to improve performance when running on a single CPU. >> >> The current implementation offers two patching variants: >> - Unwanted assembler statements like locking functions are >> overwritten >> with NOPs. When multiple instructions shall be skipped, one branch >> instruction is used instead of multiple nop instructions. > > This seems like a good idea because our spinlocks are particularly > heavyweight. > >> - Some pdtlb and pitlb instructions are patched to become pdtlb,l and >> pitlb,l which only flushes the CPU-local tlb entries instead of >> broadcasting the flush to other CPUs in the system and thus may >> improve performance. > > I really don't think this matters: on a UP system, ptdlb,l and pdtlb > are the same instruction because the CPU already knows is has no > internal CPU bus to broadcast the purge over so it in effect executes a > pdtlb,l regardless. I'd be happy to drop this part again. But is that true on a SMP system, where one has booted with maxcpus=1, too? Helge
