[PATCH] eal/riscv: implement prefetch using __builtin_prefetch

[PATCH] eal/riscv: implement prefetch using __builtin_prefetch

[dangshiwei]

RISC-V currently has no-op implementations of the rte_prefetch*
functions. Use __builtin_prefetch() to allow the compiler to emit
Zicbop prefetch instructions when the target supports them (GCC
13.1+, Clang 17.0.1+ with -march=rv*_zicbop).

The Zicbop extension has no cache-level hints, so rte_prefetch1()
and rte_prefetch2() fall back to rte_prefetch0(). The volatile
qualifier is stripped via uintptr_t cast to satisfy
__builtin_prefetch()'s const void * parameter without triggering
-Wdiscarded-qualifiers.

This replaces the abandoned v1 series by Daniel Gregory
(Message-ID: 20240530171948.19763-1-daniel.gregory@bytedance.com)
addressing reviewer feedback from Kardach and Hemminger.

Signed-off-by: dangshiwei <1138222970gg@gmail.com>
---
 lib/eal/riscv/include/rte_prefetch.h | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/lib/eal/riscv/include/rte_prefetch.h b/lib/eal/riscv/include/rte_prefetch.h
index 42146491ea..37b4787387 100644
--- a/lib/eal/riscv/include/rte_prefetch.h
+++ b/lib/eal/riscv/include/rte_prefetch.h
@@ -18,22 +18,24 @@ extern "C" {
 
 static inline void rte_prefetch0(const volatile void *p)
 {
-	RTE_SET_USED(p);
+	__builtin_prefetch((const void *)(uintptr_t)p);
 }
 
 static inline void rte_prefetch1(const volatile void *p)
 {
-	RTE_SET_USED(p);
+	/* Zicbop has no cache-level hints, fallback to rte_prefetch0 */
+	rte_prefetch0(p);
 }
 
 static inline void rte_prefetch2(const volatile void *p)
 {
-	RTE_SET_USED(p);
+	/* Zicbop has no cache-level hints, fallback to rte_prefetch0 */
+	rte_prefetch0(p);
 }
 
 static inline void rte_prefetch_non_temporal(const volatile void *p)
 {
-	/* non-temporal version not available, fallback to rte_prefetch0 */
+	/* Zicbop has no non-temporal hint, fallback to rte_prefetch0 */
 	rte_prefetch0(p);
 }
 
-- 
2.43.0

Re: [PATCH] eal/riscv: implement prefetch using __builtin_prefetch

[sunyuechi]

Hi,

In the previous prefetch discussion:

"Let's hope you get such hardware by the next release. We will need 
reviews too."

https://inbox.dpdk.org/dev/CAJFAV8zatWiYQoe4kETcM61=OS1k=QaPRsNjYSYDspKC+voiQw@mail.gmail.com/

Could you share your test environment and results?

And DPDK requires a real name in the Signed-off-by line.

Re: [PATCH] eal/riscv: implement prefetch using __builtin_prefetch

[shiwei dang]

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Hi ,

Thanks for the review. I'll address both points (real name in Signed-off-by
and test results) together in v2 once I have access to physical RISC-V
hardware.

Best regards, Dang Shiwei

On Sat, Mar 28, 2026 at 7:48 PM sunyuechi <sunyuechi@iscas.ac.cn> wrote:

> Hi,
>
> In the previous prefetch discussion:
>
> "Let's hope you get such hardware by the next release. We will need
> reviews too."
>
>
> https://inbox.dpdk.org/dev/CAJFAV8zatWiYQoe4kETcM61=OS1k=QaPRsNjYSYDspKC+voiQw@mail.gmail.com/
>
> Could you share your test environment and results?
>
> And DPDK requires a real name in the Signed-off-by line.
>
>

[-- Attachment #2: Type: text/html, Size: 1458 bytes --]

Re: [PATCH] eal/riscv: implement prefetch using __builtin_prefetch

[sunyuechi]

On 3/29/26 12:38 AM, shiwei dang wrote:

> Hi ,
>
> Thanks for the review. I'll address both points (real name in 
> Signed-off-by and test results) together in v2 once I have access to 
> physical RISC-V hardware.
>
> Best regards, Dang Shiwei
>
>

Hi,

Gentle ping — any update on v2?

Re: [PATCH] eal/riscv: implement prefetch using __builtin_prefetch

[Stephen Hemminger]

On Tue, 10 Mar 2026 21:35:24 +0800
dangshiwei <1138222970gg@gmail.com> wrote:

> RISC-V currently has no-op implementations of the rte_prefetch*
> functions. Use __builtin_prefetch() to allow the compiler to emit
> Zicbop prefetch instructions when the target supports them (GCC
> 13.1+, Clang 17.0.1+ with -march=rv*_zicbop).
> 
> The Zicbop extension has no cache-level hints, so rte_prefetch1()
> and rte_prefetch2() fall back to rte_prefetch0(). The volatile
> qualifier is stripped via uintptr_t cast to satisfy
> __builtin_prefetch()'s const void * parameter without triggering
> -Wdiscarded-qualifiers.
> 
> This replaces the abandoned v1 series by Daniel Gregory
> (Message-ID: 20240530171948.19763-1-daniel.gregory@bytedance.com)
> addressing reviewer feedback from Kardach and Hemminger.
> 
> Signed-off-by: dangshiwei <1138222970gg@gmail.com>
> ---

There is another patch for x86 that does same thing.
https://patchwork.dpdk.org/project/dpdk/patch/20250223125215.358925-2-mattias.ronnblom@ericsson.com/

Would be good to have single common file for all arch.