Hi Shanker,I'm using gcc version 5.2.0. With has_vhe() it shows the smaller code size as shown below. I tried to benchmark
On Mon, Mar 06 2017 at 2:33:18 am GMT, Shanker Donthineni <shankerd@xxxxxxxxxxxxxx> wrote:
Now all the cpu_hwcaps features have their own static keys. We don'tHow do you define "better"? Which compiler? Do you have any benchmarking data?
need a separate function hyp_alternate_select() to patch the vhe/nvhe
code. We can achieve the same functionality by using has_vhe(). It
improves the code readability, uses the jump label instructions, and
also compiler generates the better code with a fewer instructions.
Yes, it'll require a runtime check if the compiler doesn't support ASM GOTO labels.Signed-off-by: Shanker Donthineni <shankerd@xxxxxxxxxxxxxx>I have two worries about this kind of thing:
---
v2: removed 'Change-Id: Ia8084189833f2081ff13c392deb5070c46a64038' from commit
arch/arm64/kvm/hyp/debug-sr.c | 12 ++++++----
arch/arm64/kvm/hyp/switch.c | 50 +++++++++++++++++++-----------------------
arch/arm64/kvm/hyp/sysreg-sr.c | 23 +++++++++----------
3 files changed, 43 insertions(+), 42 deletions(-)
diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c
index f5154ed..e5642c2 100644
--- a/arch/arm64/kvm/hyp/debug-sr.c
+++ b/arch/arm64/kvm/hyp/debug-sr.c
@@ -109,9 +109,13 @@ static void __hyp_text __debug_save_spe_nvhe(u64 *pmscr_el1)
dsb(nsh);
}
-static hyp_alternate_select(__debug_save_spe,
- __debug_save_spe_nvhe, __debug_save_spe_vhe,
- ARM64_HAS_VIRT_HOST_EXTN);
+static void __hyp_text __debug_save_spe(u64 *pmscr_el1)
+{
+ if (has_vhe())
+ __debug_save_spe_vhe(pmscr_el1);
+ else
+ __debug_save_spe_nvhe(pmscr_el1);
+}
- Not all compilers do support jump labels, leading to a memory access
on each static key (GCC 4.8, for example). This would immediately
introduce a pretty big regression
- The hyp_alternate_select() method doesn't introduce a fast/slow path
duality. Each path has the exact same cost. I'm not keen on choosing
what is supposed to be the fast path, really.
Thanks,
M.