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* [PATCH net-next, v3] net: mana: Force full-page RX buffers for 4K page size on specific systems.
@ 2026-03-11  4:00 Dipayaan Roy
  2026-03-14 19:50 ` Jakub Kicinski
  0 siblings, 1 reply; 4+ messages in thread
From: Dipayaan Roy @ 2026-03-11  4:00 UTC (permalink / raw)
  To: kys, haiyangz, wei.liu, decui, andrew+netdev, davem, edumazet,
	kuba, pabeni, leon, longli, kotaranov, horms, shradhagupta,
	ssengar, ernis, shirazsaleem, linux-hyperv, netdev, linux-kernel,
	linux-rdma, dipayanroy

On certain systems configured with 4K PAGE_SIZE, utilizing page_pool
fragments for RX buffers results in a significant throughput regression.
Profiling reveals that this regression correlates with high overhead in the
fragment allocation and reference counting paths on these specific
platforms, rendering the multi-buffer-per-page strategy counterproductive.

To mitigate this, bypass the page_pool fragment path and force a single RX
packet per page allocation when all the following conditions are met:
  1. The system is configured with a 4K PAGE_SIZE.
  2. A processor-specific quirk is detected via SMBIOS Type 4 data.

This approach restores expected line-rate performance by ensuring
predictable RX refill behavior on affected hardware.

There is no behavioral change for systems using larger page sizes
(16K/64K), or platforms where this processor-specific quirk do not
apply.

Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Dipayaan Roy <dipayanroy@linux.microsoft.com>
---
Changes in v3:
  - changed u8* to char*
Changes in v2:
  - separate reading string index and the string, remove inline.
---
---
 .../net/ethernet/microsoft/mana/gdma_main.c   | 133 ++++++++++++++++++
 drivers/net/ethernet/microsoft/mana/mana_en.c |  23 ++-
 include/net/mana/gdma.h                       |   9 ++
 3 files changed, 163 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/microsoft/mana/gdma_main.c b/drivers/net/ethernet/microsoft/mana/gdma_main.c
index aef8612b73cb..05fecc00a90c 100644
--- a/drivers/net/ethernet/microsoft/mana/gdma_main.c
+++ b/drivers/net/ethernet/microsoft/mana/gdma_main.c
@@ -9,6 +9,7 @@
 #include <linux/msi.h>
 #include <linux/irqdomain.h>
 #include <linux/export.h>
+#include <linux/dmi.h>
 
 #include <net/mana/mana.h>
 #include <net/mana/hw_channel.h>
@@ -1959,6 +1960,128 @@ static bool mana_is_pf(unsigned short dev_id)
 	return dev_id == MANA_PF_DEVICE_ID;
 }
 
+/*
+ * Table for Processor Version strings found from SMBIOS Type 4 information,
+ * for processors that needs to force single RX buffer per page quirk for
+ * meeting line rate performance with ARM64 + 4K pages.
+ * Note: These strings are exactly matched with version fetched from SMBIOS.
+ */
+static const char * const mana_single_rxbuf_per_page_quirk_tbl[] = {
+	"Cobalt 200",
+};
+
+/* On some systems with 4K PAGE_SIZE, page_pool RX fragments can
+ * trigger a throughput regression. Hence identify those processors
+ * from the extracted SMBIOS table and apply the quirk to forces one
+ * RX buffer per page to avoid the fragment allocation/refcounting
+ * overhead in the RX refill path for those processors only.
+ */
+static bool mana_needs_single_rxbuf_per_page(struct gdma_context *gc)
+{
+	int i = 0;
+	const char *ver = gc->processor_version;
+
+	if (!ver)
+		return false;
+
+	if (PAGE_SIZE != SZ_4K)
+		return false;
+
+	while (i < ARRAY_SIZE(mana_single_rxbuf_per_page_quirk_tbl)) {
+		if (!strcmp(ver, mana_single_rxbuf_per_page_quirk_tbl[i]))
+			return true;
+		i++;
+	}
+
+	return false;
+}
+
+static void mana_get_proc_ver_strno(const struct dmi_header *hdr, void *data)
+{
+	struct gdma_context *gc = data;
+	const u8 *d = (const u8 *)hdr;
+
+	/* We are only looking for Type 4: Processor Information */
+	if (hdr->type != SMBIOS_TYPE_4_PROCESSOR_INFO)
+		return;
+
+	/* Ensure the record is long enough to contain the Processor Version
+	 * field
+	 */
+	if (hdr->length <= SMBIOS_TYPE4_PROC_VERSION_OFFSET)
+		return;
+
+	/* The 'Processor Version' string is located at index pointed by
+	 * SMBIOS_TYPE4_PROC_VERSION_OFFSET.  Make a copy of the index.
+	 * There could be multiple Type 4 tables so read and store the
+	 * processor version index found the first time.
+	 */
+	if (gc->proc_ver_strno)
+		return;
+
+	gc->proc_ver_strno = d[SMBIOS_TYPE4_PROC_VERSION_OFFSET];
+}
+
+static const char *mana_dmi_string_nosave(const struct dmi_header *hdr, u8 s)
+{
+	const char *bp = (const char *)hdr + hdr->length;
+
+	if (!s)
+		return NULL;
+
+	/* String numbers start at 1 */
+	while (--s > 0 && *bp)
+		bp += strlen(bp) + 1;
+
+	if (!*bp)
+		return NULL;
+
+	return bp;
+}
+
+static void mana_fetch_proc_ver_string(const struct dmi_header *hdr,
+				       void *data)
+{
+	struct gdma_context *gc = data;
+	const char *ver;
+
+	/* We are only looking for Type 4: Processor Information */
+	if (hdr->type != SMBIOS_TYPE_4_PROCESSOR_INFO)
+		return;
+
+	/* Extract proc version found the first time only */
+	if (!gc->proc_ver_strno || gc->processor_version)
+		return;
+
+	ver = mana_dmi_string_nosave(hdr, gc->proc_ver_strno);
+	if (ver)
+		gc->processor_version = kstrdup(ver, GFP_KERNEL);
+}
+
+/* Check and initialize all processor optimizations/quirks here */
+static bool mana_init_processor_optimization(struct gdma_context *gc)
+{
+	bool opt_initialized = false;
+
+	gc->proc_ver_strno = 0;
+	gc->processor_version = NULL;
+
+	dmi_walk(mana_get_proc_ver_strno, gc);
+	if (!gc->proc_ver_strno)
+		return false;
+
+	dmi_walk(mana_fetch_proc_ver_string, gc);
+	if (!gc->processor_version)
+		return false;
+
+	if (mana_needs_single_rxbuf_per_page(gc)) {
+		gc->force_full_page_rx_buffer = true;
+		opt_initialized = true;
+	}
+
+	return opt_initialized;
+}
+
 static int mana_gd_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 {
 	struct gdma_context *gc;
@@ -2013,6 +2136,11 @@ static int mana_gd_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 		gc->mana_pci_debugfs = debugfs_create_dir(pci_slot_name(pdev->slot),
 							  mana_debugfs_root);
 
+	if (mana_init_processor_optimization(gc))
+		dev_info(&pdev->dev,
+			 "Processor specific optimization initialized on: %s\n",
+			gc->processor_version);
+
 	err = mana_gd_setup(pdev);
 	if (err)
 		goto unmap_bar;
@@ -2055,6 +2183,8 @@ static int mana_gd_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 	pci_iounmap(pdev, bar0_va);
 free_gc:
 	pci_set_drvdata(pdev, NULL);
+	kfree(gc->processor_version);
+	gc->processor_version = NULL;
 	vfree(gc);
 release_region:
 	pci_release_regions(pdev);
@@ -2110,6 +2240,9 @@ static void mana_gd_remove(struct pci_dev *pdev)
 
 	pci_iounmap(pdev, gc->bar0_va);
 
+	kfree(gc->processor_version);
+	gc->processor_version = NULL;
+
 	vfree(gc);
 
 	pci_release_regions(pdev);
diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c
index a868c28c8280..38f94f7619ad 100644
--- a/drivers/net/ethernet/microsoft/mana/mana_en.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
@@ -744,6 +744,26 @@ static void *mana_get_rxbuf_pre(struct mana_rxq *rxq, dma_addr_t *da)
 	return va;
 }
 
+static bool
+mana_use_single_rxbuf_per_page(struct mana_port_context *apc, u32 mtu)
+{
+	struct gdma_context *gc = apc->ac->gdma_dev->gdma_context;
+
+	/* On some systems with 4K PAGE_SIZE, page_pool RX fragments can
+	 * trigger a throughput regression. Hence forces one RX buffer per page
+	 * to avoid the fragment allocation/refcounting overhead in the RX
+	 * refill path for those processors only.
+	 */
+	if (gc->force_full_page_rx_buffer)
+		return true;
+
+	/* For xdp and jumbo frames make sure only one packet fits per page. */
+	if (mtu + MANA_RXBUF_PAD > PAGE_SIZE / 2 || mana_xdp_get(apc))
+		return true;
+
+	return false;
+}
+
 /* Get RX buffer's data size, alloc size, XDP headroom based on MTU */
 static void mana_get_rxbuf_cfg(struct mana_port_context *apc,
 			       int mtu, u32 *datasize, u32 *alloc_size,
@@ -754,8 +774,7 @@ static void mana_get_rxbuf_cfg(struct mana_port_context *apc,
 	/* Calculate datasize first (consistent across all cases) */
 	*datasize = mtu + ETH_HLEN;
 
-	/* For xdp and jumbo frames make sure only one packet fits per page */
-	if (mtu + MANA_RXBUF_PAD > PAGE_SIZE / 2 || mana_xdp_get(apc)) {
+	if (mana_use_single_rxbuf_per_page(apc, mtu)) {
 		if (mana_xdp_get(apc)) {
 			*headroom = XDP_PACKET_HEADROOM;
 			*alloc_size = PAGE_SIZE;
diff --git a/include/net/mana/gdma.h b/include/net/mana/gdma.h
index ec17004b10c0..03f01496fbbf 100644
--- a/include/net/mana/gdma.h
+++ b/include/net/mana/gdma.h
@@ -9,6 +9,12 @@
 
 #include "shm_channel.h"
 
+/* SMBIOS Type 4: Processor Information table */
+#define SMBIOS_TYPE_4_PROCESSOR_INFO 4
+
+/* Byte offset containing the Processor Version string number.*/
+#define SMBIOS_TYPE4_PROC_VERSION_OFFSET 0x10
+
 #define GDMA_STATUS_MORE_ENTRIES	0x00000105
 #define GDMA_STATUS_CMD_UNSUPPORTED	0xffffffff
 
@@ -444,6 +450,9 @@ struct gdma_context {
 	struct workqueue_struct *service_wq;
 
 	unsigned long		flags;
+	char			*processor_version;
+	u8			proc_ver_strno;
+	bool			force_full_page_rx_buffer;
 };
 
 static inline bool mana_gd_is_mana(struct gdma_dev *gd)
-- 
2.34.1


^ permalink raw reply related	[flat|nested] 4+ messages in thread
end of thread, other threads:[~2026-03-21  0:29 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
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2026-03-11  4:00 [PATCH net-next, v3] net: mana: Force full-page RX buffers for 4K page size on specific systems Dipayaan Roy
2026-03-14 19:50 ` Jakub Kicinski
2026-03-20 18:37   ` Dipayaan Roy
2026-03-21  0:29     ` Jakub Kicinski

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