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

[Jun Miao]

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   |

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.

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.

So, change the 1s (MSEC_PER_SEC) -> 5ms (MSEC_PER_SEC / 200)

Signed-off-by: Jun Miao <jun.miao@xxxxxxxxx>
---
 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;
 	}
 
-- 
2.32.0