diff mbox series

[v3,net] net: mana: Fix doorbell out of order violation and avoid unnecessary doorbell rings

Message ID 1723219138-29887-1-git-send-email-longli@linuxonhyperv.com (mailing list archive)
State Accepted
Commit 58a63729c957621f1990c3494c702711188ca347
Delegated to: Netdev Maintainers
Headers show
Series [v3,net] net: mana: Fix doorbell out of order violation and avoid unnecessary doorbell rings | expand

Checks

Context Check Description
netdev/series_format success Single patches do not need cover letters
netdev/tree_selection success Clearly marked for net
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag present in non-next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 29 this patch: 29
netdev/build_tools success Errors and warnings before: 9 this patch: 9
netdev/cc_maintainers warning 1 maintainers not CCed: sharmaajay@microsoft.com
netdev/build_clang success Errors and warnings before: 29 this patch: 29
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success Fixes tag looks correct
netdev/build_allmodconfig_warn success Errors and warnings before: 29 this patch: 29
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 45 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
netdev/contest success net-next-2024-08-10--18-00 (tests: 707)

Commit Message

Long Li Aug. 9, 2024, 3:58 p.m. UTC 
From: Long Li <longli@microsoft.com>

After napi_complete_done() is called when NAPI is polling in the current
process context, another NAPI may be scheduled and start running in
softirq on another CPU and may ring the doorbell before the current CPU
does. When combined with unnecessary rings when there is no need to arm
the CQ, it triggers error paths in the hardware.

This patch fixes this by calling napi_complete_done() after doorbell
rings. It limits the number of unnecessary rings when there is
no need to arm. MANA hardware specifies that there must be one doorbell
ring every 8 CQ wraparounds. This driver guarantees one doorbell ring as
soon as the number of consumed CQEs exceeds 4 CQ wraparounds. In practical
workloads, the 4 CQ wraparounds proves to be big enough that it rarely
exceeds this limit before all the napi weight is consumed.

To implement this, add a per-CQ counter cq->work_done_since_doorbell,
and make sure the CQ is armed as soon as passing 4 wraparounds of the CQ.

Cc: stable@vger.kernel.org
Fixes: e1b5683ff62e ("net: mana: Move NAPI from EQ to CQ")
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Long Li <longli@microsoft.com>
---
change in v2:
Added more details to comments to explain the patch.

change in v3:
Corrected typo. Removed extra empty lines between "Fixes" and "Reviewed-by".

 drivers/net/ethernet/microsoft/mana/mana_en.c | 24 ++++++++++++-------
 include/net/mana/mana.h                       |  1 +
 2 files changed, 16 insertions(+), 9 deletions(-)

Comments

patchwork-bot+netdevbpf@kernel.org Aug. 13, 2024, 11:30 a.m. UTC | #1 
Hello:

This patch was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Fri,  9 Aug 2024 08:58:58 -0700 you wrote:
> From: Long Li <longli@microsoft.com>
> 
> After napi_complete_done() is called when NAPI is polling in the current
> process context, another NAPI may be scheduled and start running in
> softirq on another CPU and may ring the doorbell before the current CPU
> does. When combined with unnecessary rings when there is no need to arm
> the CQ, it triggers error paths in the hardware.
> 
> [...]

Here is the summary with links:
  - [v3,net] net: mana: Fix doorbell out of order violation and avoid unnecessary doorbell rings
    https://git.kernel.org/netdev/net/c/58a63729c957

You are awesome, thank you!
diff mbox series

Patch

diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c
index d2f07e179e86..f83211f9e737 100644
--- a/drivers/net/ethernet/microsoft/mana/mana_en.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
@@ -1788,7 +1788,6 @@  static void mana_poll_rx_cq(struct mana_cq *cq)
 static int mana_cq_handler(void *context, struct gdma_queue *gdma_queue)
 {
 	struct mana_cq *cq = context;
-	u8 arm_bit;
 	int w;
 
 	WARN_ON_ONCE(cq->gdma_cq != gdma_queue);
@@ -1799,16 +1798,23 @@  static int mana_cq_handler(void *context, struct gdma_queue *gdma_queue)
 		mana_poll_tx_cq(cq);
 
 	w = cq->work_done;
-
-	if (w < cq->budget &&
-	    napi_complete_done(&cq->napi, w)) {
-		arm_bit = SET_ARM_BIT;
-	} else {
-		arm_bit = 0;
+	cq->work_done_since_doorbell += w;
+
+	if (w < cq->budget) {
+		mana_gd_ring_cq(gdma_queue, SET_ARM_BIT);
+		cq->work_done_since_doorbell = 0;
+		napi_complete_done(&cq->napi, w);
+	} else if (cq->work_done_since_doorbell >
+		   cq->gdma_cq->queue_size / COMP_ENTRY_SIZE * 4) {
+		/* MANA hardware requires at least one doorbell ring every 8
+		 * wraparounds of CQ even if there is no need to arm the CQ.
+		 * This driver rings the doorbell as soon as we have exceeded
+		 * 4 wraparounds.
+		 */
+		mana_gd_ring_cq(gdma_queue, 0);
+		cq->work_done_since_doorbell = 0;
 	}
 
-	mana_gd_ring_cq(gdma_queue, arm_bit);
-
 	return w;
 }
 
diff --git a/include/net/mana/mana.h b/include/net/mana/mana.h
index 6439fd8b437b..7caa334f4888 100644
--- a/include/net/mana/mana.h
+++ b/include/net/mana/mana.h
@@ -275,6 +275,7 @@  struct mana_cq {
 	/* NAPI data */
 	struct napi_struct napi;
 	int work_done;
+	int work_done_since_doorbell;
 	int budget;
 };