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SubjectRe: [PATCH] ena: Speed up initialization 90x by reducing poll delays
Date

On 2/28/20, 4:29 PM, "Josh Triplett" <josh@joshtriplett.org> wrote:

Before initializing completion queue interrupts, the ena driver uses
polling to wait for responses on the admin command queue. The ena driver
waits 5ms between polls, but the hardware has generally finished long
before that. Reduce the poll time to 10us.

On a c5.12xlarge, this improves ena initialization time from 173.6ms to
1.920ms, an improvement of more than 90x. This improves server boot time
and time to network bringup.

Thanks Josh,
We agree that polling rate should be increased, but prefer not to do it aggressively and blindly.
For example linear backoff approach might be a better choice. Please let us re-work a little this
patch and bring it to review. Thanks!

Before:
[ 0.531722] calling ena_init+0x0/0x63 @ 1
[ 0.531722] ena: Elastic Network Adapter (ENA) v2.1.0K
[ 0.531751] ena 0000:00:05.0: Elastic Network Adapter (ENA) v2.1.0K
[ 0.531946] PCI Interrupt Link [LNKD] enabled at IRQ 11
[ 0.547425] ena: ena device version: 0.10
[ 0.547427] ena: ena controller version: 0.0.1 implementation version 1
[ 0.709497] ena 0000:00:05.0: Elastic Network Adapter (ENA) found at mem febf4000, mac addr 06:c4:22:0e:dc:da, Placement policy: Low Latency
[ 0.709508] initcall ena_init+0x0/0x63 returned 0 after 173616 usecs

After:
[ 0.526965] calling ena_init+0x0/0x63 @ 1
[ 0.526966] ena: Elastic Network Adapter (ENA) v2.1.0K
[ 0.527056] ena 0000:00:05.0: Elastic Network Adapter (ENA) v2.1.0K
[ 0.527196] PCI Interrupt Link [LNKD] enabled at IRQ 11
[ 0.527211] ena: ena device version: 0.10
[ 0.527212] ena: ena controller version: 0.0.1 implementation version 1
[ 0.528925] ena 0000:00:05.0: Elastic Network Adapter (ENA) found at mem febf4000, mac addr 06:c4:22:0e:dc:da, Placement policy: Low Latency
[ 0.528934] initcall ena_init+0x0/0x63 returned 0 after 1920 usecs

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
---
drivers/net/ethernet/amazon/ena/ena_com.c | 22 ++++++++++++----------
1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ethernet/amazon/ena/ena_com.c b/drivers/net/ethernet/amazon/ena/ena_com.c
index 1fb58f9ad80b..203b2130d707 100644
--- a/drivers/net/ethernet/amazon/ena/ena_com.c
+++ b/drivers/net/ethernet/amazon/ena/ena_com.c
@@ -62,7 +62,7 @@

#define ENA_REGS_ADMIN_INTR_MASK 1

-#define ENA_POLL_MS 5
+#define ENA_POLL_US 10

/*****************************************************************************/
/*****************************************************************************/
@@ -572,7 +572,7 @@ static int ena_com_wait_and_process_admin_cq_polling(struct ena_comp_ctx *comp_c
goto err;
}

- msleep(ENA_POLL_MS);
+ usleep_range(ENA_POLL_US, 2 * ENA_POLL_US);
}
if (unlikely(comp_ctx->status == ENA_CMD_ABORTED)) {
@@ -943,12 +943,13 @@ static void ena_com_io_queue_free(struct ena_com_dev *ena_dev,
static int wait_for_reset_state(struct ena_com_dev *ena_dev, u32 timeout,
u16 exp_state)
{
- u32 val, i;
+ u32 val;
+ unsigned long timeout_jiffies;

- /* Convert timeout from resolution of 100ms to ENA_POLL_MS */
- timeout = (timeout * 100) / ENA_POLL_MS;
+ /* Convert timeout from resolution of 100ms */
+ timeout_jiffies = jiffies + msecs_to_jiffies(timeout * 100);
- for (i = 0; i < timeout; i++) {
+ while (1) {
val = ena_com_reg_bar_read32(ena_dev, ENA_REGS_DEV_STS_OFF);
if (unlikely(val == ENA_MMIO_READ_TIMEOUT)) {
@@ -960,10 +961,11 @@ static int wait_for_reset_state(struct ena_com_dev *ena_dev, u32 timeout,
exp_state)
return 0;

- msleep(ENA_POLL_MS);
- }
+ if (time_is_before_jiffies(timeout_jiffies))
+ return -ETIME;

- return -ETIME;
+ usleep_range(ENA_POLL_US, 2 * ENA_POLL_US);
+ }
}
static bool ena_com_check_supported_feature_id(struct ena_com_dev *ena_dev,
@@ -1458,7 +1460,7 @@ void ena_com_wait_for_abort_completion(struct ena_com_dev *ena_dev)
spin_lock_irqsave(&admin_queue->q_lock, flags);
while (atomic_read(&admin_queue->outstanding_cmds) != 0) {
spin_unlock_irqrestore(&admin_queue->q_lock, flags);
- msleep(ENA_POLL_MS);
+ usleep_range(ENA_POLL_US, 2 * ENA_POLL_US);
spin_lock_irqsave(&admin_queue->q_lock, flags);
}
spin_unlock_irqrestore(&admin_queue->q_lock, flags);
--
2.25.1


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