Re: [PATCH 1/1] virt: tdx-guest: Optimize the get-quote polling interval time

[Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>]

Hi Miao,

On 2/11/2026 12:58 AM, Jun Miao wrote:
> The TD guest sends TDREPORT to the TD Quoting Enclave via a vsock or
> a tdvmcall. In general, vsock is indeed much faster than tdvmcall,
> and Quote requests usually take a few millisecond to complete rather
> than seconds based on actual measurements.
> 
> The following get quote time via tdvmcall were obtained on the GNR:
> 
> | msleep_interruptible(time)     | 1s       | 5ms      | 1ms        |
> | ------------------------------ | -------- | -------- | ---------- |
> | Duration                       | 1.004 s  | 1.005 s  | 1.036 s    |
> | Total(Get Quote)               | 167      | 142      | 167        |
> | Success:                       | 167      | 142      | 167        |
> | Failure:                       | 0        | 0        | 0          |
> | Avg total / 1s                 | 0.97     | 141.31   | 166.35     |
> | Avg success / 1s               | 0.97     | 141.31   | 166.35     |
> | Avg total / 1s / thread        | 0.97     | 141.31   | 166.35     |
> | Avg success / 1s / thread      | 0.97     | 141.31   | 166.35     |
> | Min elapsed_time               | 1025.95ms| 6.85 ms  | 2.99 ms    |
> | Max elapsed_time               | 1025.95ms| 10.93 ms | 10.76 ms   |
> 

Thanks for sharing the data!

> According to trace analysis, the typical execution tdvmcall get the
> quote time is 4 ms. Therefore, 5 ms is a reasonable balance between
> performance efficiency and CPU overhead.

Since the average is 4 ms, why choose 5ms?

> 
> And compared to the previous throughput of one request per second,
> the current 5ms can get 142 requests per second delivers a
> 142× performance improvement, which is critical for high-frequency
> use cases without vsock.

Is this addressing a real customer issue or a theoretical improvement? 
If this is solving a real problem, could you share more details about
the use case and Quoting Service implementation you're testing against?

I ask because the Quote completion time depends heavily on the Quoting
Service implementation, which varies by deployment. Since we're optimizing
for performance, I'm wondering if we should consider an interrupt-based
approach using the SetupEventNotifyInterrupt TDVMCALL instead of polling.

> 
> So, change the 1s (MSEC_PER_SEC) -> 5ms (MSEC_PER_SEC / 200)
> 
> Signed-off-by: Jun Miao <jun.miao@intel.com>
> ---
>  drivers/virt/coco/tdx-guest/tdx-guest.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/virt/coco/tdx-guest/tdx-guest.c b/drivers/virt/coco/tdx-guest/tdx-guest.c
> index 4e239ec960c9..71d2d7304b1a 100644
> --- a/drivers/virt/coco/tdx-guest/tdx-guest.c
> +++ b/drivers/virt/coco/tdx-guest/tdx-guest.c
> @@ -251,11 +251,11 @@ static int wait_for_quote_completion(struct tdx_quote_buf *quote_buf, u32 timeou
>  	int i = 0;
>  
>  	/*
> -	 * Quote requests usually take a few seconds to complete, so waking up
> -	 * once per second to recheck the status is fine for this use case.
> +	 * Quote requests usually take a few milliseconds to complete, so waking up
> +	 * once per 5 milliseconds to recheck the status is fine for this use case.
>  	 */
> -	while (quote_buf->status == GET_QUOTE_IN_FLIGHT && i++ < timeout) {
> -		if (msleep_interruptible(MSEC_PER_SEC))
> +	while (quote_buf->status == GET_QUOTE_IN_FLIGHT && i++ < 200 * timeout) {
> +		if (msleep_interruptible(MSEC_PER_SEC / 200))
>  			return -EINTR;
>  	}
>  

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer