Re: [net-next,v2] net: mana: Force full-page RX buffers for 4K page size on specific systems.

[Paolo Abeni <pabeni@redhat.com>]

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---
net: mana: Force full-page RX buffers for 4K page size on specific systems.

This commit adds processor-specific optimization for ARM64 systems with
4K pages where page_pool fragments cause throughput regression. It
detects affected processors via SMBIOS and forces one RX buffer per page.

> 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

[ ... ]

> @@ -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 ea71de39f996..f17cc2cc7dd9 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..be56b347f3f6 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;
> +	u8			*processor_version;
> +	u8			proc_ver_strno;
> +	bool			force_full_page_rx_buffer;
>  };
>
>  static inline bool mana_gd_is_mana(struct gdma_dev *gd)

Should processor_version be declared as char * instead of u8 *?

The field is used as a string throughout the code: it's assigned from
kstrdup() in mana_fetch_proc_ver_string(), read as const char *ver
in mana_needs_single_rxbuf_per_page(), passed to strcmp(), and printed
with %s format in dev_info().

Using u8 * for string data can trigger compiler warnings with
-Wpointer-sign, since string functions expect char * types.