[PATCH] Add a counter and debug printf to change the latency inside tlb_sync

[Jessica Clarke]

On 10 Jan 2025, at 00:03, Chao-ying Fu <icebergfu at gmail.com> wrote:
> 
> The tlb_sync loop is slowed down by variable latency to avoid
> livelock on some platforms.

I don’t understand “by variable latency”. It doesn’t do anything but
print.

> ---
> lib/sbi/sbi_tlb.c | 6 ++++++
> 1 file changed, 6 insertions(+)
> 
> diff --git a/lib/sbi/sbi_tlb.c b/lib/sbi/sbi_tlb.c
> index 01b31f4..d46b95c 100644
> --- a/lib/sbi/sbi_tlb.c
> +++ b/lib/sbi/sbi_tlb.c
> @@ -247,6 +247,7 @@ static void tlb_process(struct sbi_scratch *scratch)
> 
> static void tlb_sync(struct sbi_scratch *scratch)
> {
> + int count = 0;
> atomic_t *tlb_sync =
> sbi_scratch_offset_ptr(scratch, tlb_sync_off);
> 
> @@ -256,6 +257,11 @@ static void tlb_sync(struct sbi_scratch *scratch)
> * consume fifo requests to avoid deadlock.
> */
> tlb_process_once(scratch);
> + count++;

Technically this could overflow, and count is signed, so UB...

> + if ((count % 20) == 0) {
> + sbi_dprintf("tlb_sync loop count = %d value = %ld\n",
> +    count, atomic_read(tlb_sync));

What value does this add? 20 isn’t that big...

If your goal is to avoid spinning and hammering memory, use pause?

Jess

> + }
> }
> 
> return;
> -- 
> 2.47.1
> 
> 
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