From: Koichiro Den <den@valinux.co.jp>
To: "Jon Mason" <jdmason@kudzu.us>,
"Dave Jiang" <dave.jiang@intel.com>,
"Allen Hubbe" <allenbh@gmail.com>,
"Manivannan Sadhasivam" <mani@kernel.org>,
"Krzysztof Wilczyński" <kwilczynski@kernel.org>,
"Kishon Vijay Abraham I" <kishon@kernel.org>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Frank Li" <Frank.Li@nxp.com>,
"Jerome Brunet" <jbrunet@baylibre.com>,
"Lorenzo Pieralisi" <lpieralisi@kernel.org>,
"Niklas Cassel" <cassel@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
ntb@lists.linux.dev
Subject: [PATCH v3 02/10] PCI: endpoint: pci-epf-vntb: Defer pci_epc_raise_irq() out of atomic context
Date: Mon, 23 Mar 2026 12:15:36 +0900 [thread overview]
Message-ID: <20260323031544.2598111-3-den@valinux.co.jp> (raw)
In-Reply-To: <20260323031544.2598111-1-den@valinux.co.jp>
The NTB .peer_db_set() callback may be invoked from atomic context.
pci-epf-vntb currently calls pci_epc_raise_irq() directly, but
pci_epc_raise_irq() may sleep (it takes epc->lock).
Avoid sleeping in atomic context by coalescing doorbell bits into an
atomic64 pending mask and raising MSIs from a work item. Limit the
amount of work per run to avoid monopolizing the workqueue under a
doorbell storm.
Fixes: e35f56bb0330 ("PCI: endpoint: Support NTB transfer between RC and EP")
Signed-off-by: Koichiro Den <den@valinux.co.jp>
---
Changes since v2:
- Resolved a trivial context-only conflict after
d799984233a5 ("PCI: endpoint: pci-epf-vntb: Stop cmd_handler work in epf_ntb_epc_cleanup")
landed in pci/endpoint.
drivers/pci/endpoint/functions/pci-epf-vntb.c | 106 +++++++++++++-----
1 file changed, 78 insertions(+), 28 deletions(-)
diff --git a/drivers/pci/endpoint/functions/pci-epf-vntb.c b/drivers/pci/endpoint/functions/pci-epf-vntb.c
index a75f8a30f8dc..bc3b3df53ddb 100644
--- a/drivers/pci/endpoint/functions/pci-epf-vntb.c
+++ b/drivers/pci/endpoint/functions/pci-epf-vntb.c
@@ -69,6 +69,9 @@ static struct workqueue_struct *kpcintb_workqueue;
#define MAX_DB_COUNT 32
#define MAX_MW 4
+/* Limit per-work execution to avoid monopolizing kworker on doorbell storms. */
+#define VNTB_PEER_DB_WORK_BUDGET 5
+
enum epf_ntb_bar {
BAR_CONFIG,
BAR_DB,
@@ -129,6 +132,8 @@ struct epf_ntb {
u32 spad_count;
u64 mws_size[MAX_MW];
atomic64_t db;
+ atomic64_t peer_db_pending;
+ struct work_struct peer_db_work;
u32 vbus_number;
u16 vntb_pid;
u16 vntb_vid;
@@ -920,6 +925,8 @@ static int epf_ntb_epc_init(struct epf_ntb *ntb)
INIT_DELAYED_WORK(&ntb->cmd_handler, epf_ntb_cmd_handler);
queue_work(kpcintb_workqueue, &ntb->cmd_handler.work);
+ enable_work(&ntb->peer_db_work);
+
return 0;
err_write_header:
@@ -943,6 +950,7 @@ static int epf_ntb_epc_init(struct epf_ntb *ntb)
static void epf_ntb_epc_cleanup(struct epf_ntb *ntb)
{
disable_delayed_work_sync(&ntb->cmd_handler);
+ disable_work_sync(&ntb->peer_db_work);
epf_ntb_mw_bar_clear(ntb, ntb->num_mws);
epf_ntb_db_bar_clear(ntb);
epf_ntb_config_sspad_bar_clear(ntb);
@@ -1357,41 +1365,79 @@ static int vntb_epf_peer_spad_write(struct ntb_dev *ndev, int pidx, int idx, u32
return 0;
}
+static void vntb_epf_peer_db_work(struct work_struct *work)
+{
+ struct epf_ntb *ntb = container_of(work, struct epf_ntb, peer_db_work);
+ struct pci_epf *epf = ntb->epf;
+ unsigned int budget = VNTB_PEER_DB_WORK_BUDGET;
+ u8 func_no, vfunc_no;
+ u32 interrupt_num;
+ u64 db_bits;
+ int ret;
+
+ if (!epf || !epf->epc)
+ return;
+
+ func_no = epf->func_no;
+ vfunc_no = epf->vfunc_no;
+
+ /*
+ * Drain doorbells from peer_db_pending in snapshots (atomic64_xchg()).
+ * Limit the number of snapshots handled per run so we don't monopolize
+ * the workqueue under a doorbell storm.
+ */
+ while (budget--) {
+ db_bits = atomic64_xchg(&ntb->peer_db_pending, 0);
+ if (!db_bits)
+ return;
+
+ while (db_bits) {
+ /*
+ * pci_epc_raise_irq() for MSI expects a 1-based
+ * interrupt number. ffs() returns a 1-based index (bit
+ * 0 -> 1). We historically add +2 to compute
+ * interrupt_num.
+ *
+ * Legacy mapping (kept for compatibility):
+ *
+ * MSI #1 : link event (reserved)
+ * MSI #2 : unused (historical offset)
+ * MSI #3 : doorbell bit 0 (DB#0)
+ * MSI #4 : doorbell bit 1 (DB#1)
+ * ...
+ *
+ * Do not change this mapping to avoid breaking
+ * interoperability with older peers.
+ */
+ interrupt_num = ffs(db_bits) + 2;
+ db_bits &= db_bits - 1;
+
+ ret = pci_epc_raise_irq(epf->epc, func_no, vfunc_no,
+ PCI_IRQ_MSI, interrupt_num);
+ if (ret)
+ dev_err(&ntb->ntb.dev,
+ "Failed to raise IRQ for interrupt_num %u: %d\n",
+ interrupt_num, ret);
+ }
+ }
+
+ if (atomic64_read(&ntb->peer_db_pending))
+ queue_work(kpcintb_workqueue, &ntb->peer_db_work);
+}
+
static int vntb_epf_peer_db_set(struct ntb_dev *ndev, u64 db_bits)
{
- u32 interrupt_num = ffs(db_bits) + 1;
struct epf_ntb *ntb = ntb_ndev(ndev);
- u8 func_no, vfunc_no;
- int ret;
-
- func_no = ntb->epf->func_no;
- vfunc_no = ntb->epf->vfunc_no;
/*
- * pci_epc_raise_irq() for MSI expects a 1-based interrupt number.
- * ffs() returns a 1-based index (bit 0 -> 1). interrupt_num has already
- * been computed as ffs(db_bits) + 1 above. Adding one more +1 when
- * calling pci_epc_raise_irq() therefore results in:
- *
- * doorbell bit 0 -> MSI #3
- *
- * Legacy mapping (kept for compatibility):
- *
- * MSI #1 : link event (reserved)
- * MSI #2 : unused (historical offset)
- * MSI #3 : doorbell bit 0 (DB#0)
- * MSI #4 : doorbell bit 1 (DB#1)
- * ...
- *
- * Do not change this mapping to avoid breaking interoperability with
- * older peers.
+ * .peer_db_set() may be called from atomic context. pci_epc_raise_irq()
+ * can sleep (it takes epc->lock), so defer MSI raising to process
+ * context. Doorbell requests are coalesced in peer_db_pending.
*/
- ret = pci_epc_raise_irq(ntb->epf->epc, func_no, vfunc_no,
- PCI_IRQ_MSI, interrupt_num + 1);
- if (ret)
- dev_err(&ntb->ntb.dev, "Failed to raise IRQ\n");
+ atomic64_or(db_bits, &ntb->peer_db_pending);
+ queue_work(kpcintb_workqueue, &ntb->peer_db_work);
- return ret;
+ return 0;
}
static u64 vntb_epf_db_read(struct ntb_dev *ndev)
@@ -1629,6 +1675,10 @@ static int epf_ntb_probe(struct pci_epf *epf,
ntb->epf = epf;
ntb->vbus_number = 0xff;
+ INIT_WORK(&ntb->peer_db_work, vntb_epf_peer_db_work);
+ disable_work(&ntb->peer_db_work);
+ atomic64_set(&ntb->peer_db_pending, 0);
+
/* Initially, no bar is assigned */
for (i = 0; i < VNTB_BAR_NUM; i++)
ntb->epf_ntb_bar[i] = NO_BAR;
--
2.51.0
next prev parent reply other threads:[~2026-03-23 3:16 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-23 3:15 [PATCH v3 00/10] PCI: endpoint: pci-epf-vntb / NTB: epf: Enable per-doorbell bit handling Koichiro Den
2026-03-23 3:15 ` [PATCH v3 01/10] PCI: endpoint: pci-epf-vntb: Document legacy MSI doorbell offset Koichiro Den
2026-03-23 3:15 ` Koichiro Den [this message]
2026-03-23 18:27 ` [PATCH v3 02/10] PCI: endpoint: pci-epf-vntb: Defer pci_epc_raise_irq() out of atomic context Frank Li
2026-05-01 16:26 ` Manivannan Sadhasivam
2026-05-11 7:54 ` Koichiro Den
2026-03-23 3:15 ` [PATCH v3 03/10] PCI: endpoint: pci-epf-vntb: Report 0-based doorbell vector via ntb_db_event() Koichiro Den
2026-03-23 3:15 ` [PATCH v3 04/10] PCI: endpoint: pci-epf-vntb: Exclude reserved slots from db_valid_mask Koichiro Den
2026-03-23 3:15 ` [PATCH v3 05/10] PCI: endpoint: pci-epf-vntb: Implement db_vector_count/mask for doorbells Koichiro Den
2026-03-23 3:15 ` [PATCH v3 06/10] NTB: epf: Document legacy doorbell slot offset in ntb_epf_peer_db_set() Koichiro Den
2026-03-23 3:15 ` [PATCH v3 07/10] NTB: epf: Make db_valid_mask cover only real doorbell bits Koichiro Den
2026-03-23 3:15 ` [PATCH v3 08/10] NTB: epf: Report 0-based doorbell vector via ntb_db_event() Koichiro Den
2026-03-23 3:15 ` [PATCH v3 09/10] NTB: epf: Fix doorbell bitmask handling in db_read/db_clear Koichiro Den
2026-05-01 16:29 ` Manivannan Sadhasivam
2026-05-11 9:15 ` Koichiro Den
2026-03-23 3:15 ` [PATCH v3 10/10] NTB: epf: Implement db_vector_count/mask for doorbells Koichiro Den
2026-03-23 15:43 ` [PATCH v3 00/10] PCI: endpoint: pci-epf-vntb / NTB: epf: Enable per-doorbell bit handling Koichiro Den
2026-03-25 6:23 ` Niklas Cassel
2026-03-25 8:44 ` Koichiro Den
2026-04-07 15:21 ` Koichiro Den
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20260323031544.2598111-3-den@valinux.co.jp \
--to=den@valinux.co.jp \
--cc=Frank.Li@nxp.com \
--cc=allenbh@gmail.com \
--cc=bhelgaas@google.com \
--cc=cassel@kernel.org \
--cc=dave.jiang@intel.com \
--cc=jbrunet@baylibre.com \
--cc=jdmason@kudzu.us \
--cc=kishon@kernel.org \
--cc=kwilczynski@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pci@vger.kernel.org \
--cc=lpieralisi@kernel.org \
--cc=mani@kernel.org \
--cc=ntb@lists.linux.dev \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).