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Date: Tue, 5 Mar 2024 16:27:50 -0800 From: William Tu <witu@...dia.com> To: Jakub Kicinski <kuba@...nel.org> Cc: netdev@...r.kernel.org, jiri@...dia.com, bodong@...dia.com, tariqt@...dia.com, yossiku@...dia.com Subject: Re: [PATCH RFC v2 net-next 1/2] devlink: Add shared descriptor eswitch attr On 3/4/24 8:37 PM, Jakub Kicinski wrote: > External email: Use caution opening links or attachments > > > On Fri, 1 Mar 2024 03:11:18 +0200 William Tu wrote: >> Add two eswitch attrs: shrdesc_mode and shrdesc_count. >> >> 1. shrdesc_mode: to enable a sharing memory buffer for >> representor's rx buffer, > Let's narrow down the terminology. "Shared memory buffer" > and "shared memory pool" and "shrdesc" all refer to the same > thing. Let's stick to shared pool? ok, will use share pool. >> and 2. shrdesc_count: to control the >> number of buffers in this shared memory pool. > _default_ number of buffers in shared pool used by representors? > > If/when the API to configure shared pools becomes real it will > presumably take precedence over this default? yes, if that's the case. >> When using switchdev mode, the representor ports handles the slow path >> traffic, the traffic that can't be offloaded will be redirected to the >> representor port for processing. Memory consumption of the representor >> port's rx buffer can grow to several GB when scaling to 1k VFs reps. >> For example, in mlx5 driver, each RQ, with a typical 1K descriptors, >> consumes 3MB of DMA memory for packet buffer in WQEs, and with four >> channels, it consumes 4 * 3MB * 1024 = 12GB of memory. And since rep >> ports are for slow path traffic, most of these rx DMA memory are idle. >> >> Add shrdesc_mode configuration, allowing multiple representors >> to share a rx memory buffer pool. When enabled, individual representor >> doesn't need to allocate its dedicated rx buffer, but just pointing >> its rq to the memory pool. This could make the memory being better >> utilized. The shrdesc_count represents the number of rx ring >> entries, e.g., same meaning as ethtool -g, that's shared across other >> representors. Users adjust it based on how many reps, total system >> memory, or performance expectation. > Can we use bytes as the unit? Like the page pool. Descriptors don't > mean much to the user. But how about the unit size? do we assume unit size = 1 page? so page pool has order: 2^order pages on allocation pool_size: size of ptr_ring How about we assume that order is 0, and let user set pool_size (number of page-size entries). > >> The two params are also useful for other vendors such as Intel ICE >> drivers and Broadcom's driver, which also have representor ports for >> slow path traffic. >> >> An example use case: >> $ devlink dev eswitch show pci/0000:08:00.0 >> pci/0000:08:00.0: mode legacy inline-mode none encap-mode basic \ >> shrdesc-mode none shrdesc-count 0 >> $ devlink dev eswitch set pci/0000:08:00.0 mode switchdev \ >> shrdesc-mode basic shrdesc-count 1024 >> $ devlink dev eswitch show pci/0000:08:00.0 >> pci/0000:08:00.0: mode switchdev inline-mode none encap-mode basic \ >> shrdesc-mode basic shrdesc-count 1024 >> >> Note that new configurations are set at legacy mode, and enabled at >> switchdev mode. >> Documentation/netlink/specs/devlink.yaml | 17 ++++++++++ >> include/net/devlink.h | 8 +++++ >> include/uapi/linux/devlink.h | 7 ++++ >> net/devlink/dev.c | 43 ++++++++++++++++++++++++ >> net/devlink/netlink_gen.c | 6 ++-- >> 5 files changed, 79 insertions(+), 2 deletions(-) > ENODOCS will add docs in next version, thanks. >> diff --git a/Documentation/netlink/specs/devlink.yaml b/Documentation/netlink/specs/devlink.yaml >> index cf6eaa0da821..58f31d99b8b3 100644 >> --- a/Documentation/netlink/specs/devlink.yaml >> +++ b/Documentation/netlink/specs/devlink.yaml >> @@ -119,6 +119,14 @@ definitions: >> name: none >> - >> name: basic >> + - >> + type: enum >> + name: eswitch-shrdesc-mode >> + entries: >> + - >> + name: none >> + - >> + name: basic > Do we need this knob? > Can we not assume that shared-pool-count == 0 means disabled? do you mean assume or not assume? I guess you mean assume, so use "shared-pool-count == 0" to indicate disable? That will also work so we only need to introduce 1 attribute. > We can always add the knob later if needed, right now it's > just on / off with some less direct names. > >> - >> type: enum >> name: dpipe-header-id >> @@ -429,6 +437,13 @@ attribute-sets: >> name: eswitch-encap-mode >> type: u8 >> enum: eswitch-encap-mode >> + - >> + name: eswitch-shrdesc-mode >> + type: u8 > u32, netlink rounds sizes up to 4B, anyway ok, thanks! > >> + enum: eswitch-shrdesc-mode >> + - >> + name: eswitch-shrdesc-count >> + type: u32 >> - >> name: resource-list >> type: nest
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