On 7/31/19 12:33 AM, Chris Wilson wrote:
Quoting Daniele Ceraolo Spurio (2019-07-31 01:49:01)
@@ -1401,7 +1453,7 @@ static void process_csb(struct intel_engine_cs *engine)
engine->name, head,
buf[2 * head + 0], buf[2 * head + 1]);
- switch (csb_parse(execlists, buf + 2 * head)) {
+ switch (execlists->csb_parse(execlists, buf + 2 * head)) {
So I worry about the cost of a retpoline here (tucked away inside an
irqs-off loop), and whether a local func avoids the retpoline or if we
just have to use an if-ladder.
-Chris
I've tried with:
static enum intel_csb_step
(*csb_parse[])(const struct intel_engine_execlists *, const u32 *) = {
[CSB_GEN8] = gen8_csb_parse,
[CSB_GEN12] = gen12_csb_parse,
};
switch (csb_parse[execlists->csb_format](..))
But AFAICS from the objdump the assembly code generated with GCC 8.3 and
CONFIG_RETPOLINE=y is more or less the same, there is just 2 extra mov
instructions when using the array of functions. I can't spot the
retpoline in neither case thought, so not sure if I'm missing something.
Should I just go with an if-else?
Daniele
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