On 2024/12/11 8:51 PM, Craig Blackmore wrote:
Calling `vext_continuous_ldst_tlb` for load/stores smaller than 12 bytes
significantly improves performance.
Co-authored-by: Helene CHELIN <helene.che...@embecosm.com>
Co-authored-by: Paolo Savini <paolo.sav...@embecosm.com>
Co-authored-by: Craig Blackmore <craig.blackm...@embecosm.com>
Signed-off-by: Helene CHELIN <helene.che...@embecosm.com>
Signed-off-by: Paolo Savini <paolo.sav...@embecosm.com>
Signed-off-by: Craig Blackmore <craig.blackm...@embecosm.com>
---
target/riscv/vector_helper.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/target/riscv/vector_helper.c b/target/riscv/vector_helper.c
index 0f57e48cc5..529b4b261e 100644
--- a/target/riscv/vector_helper.c
+++ b/target/riscv/vector_helper.c
@@ -393,6 +393,22 @@ vext_ldst_us(void *vd, target_ulong base, CPURISCVState
*env, uint32_t desc,
return;
}
+#if defined(CONFIG_USER_ONLY)
+ /*
+ * For data sizes < 12 bits we get better performance by simply calling
I think that the `bits` should be replaced with `bytes` here.
It seems that this patch aims to strike a balance between the overhead
of checking and probing for the fast path and
the benefits of directly executing load/store operations through the
slow path.
Could you please share any experiment results (and the steps/commands)
that illustrate the performance impact when the load/store size exceeds
12 bytes?
(BTW, this version can pass the vstart test case that I created for the
unexpected vstart value issue in the previous version.)
(https://github.com/rnax/rise-rvv-tcg-qemu-tooling/commit/bccc43a7be9f636cfdaea3c2bfb020558777c7dc)
+ * vext_continuous_ldst_tlb
+ */
+ if (nf == 1 && (evl << log2_esz) < 12) {
+ addr = base + (env->vstart << log2_esz);
+ vext_continuous_ldst_tlb(env, ldst_tlb, vd, evl, addr, env->vstart, ra,
+ esz, is_load);
+
+ env->vstart = 0;
+ vext_set_tail_elems_1s(evl, vd, desc, nf, esz, max_elems);
+ return;
+ }
+#endif
+
/* Calculate the page range of first page */
addr = base + ((env->vstart * nf) << log2_esz);
page_split = -(addr | TARGET_PAGE_MASK);
