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c72568c21b
enqueue_to_backlog() is showing up in kernel profiles on hosts with many cores, when RFS/RPS is used. The following softnet_data fields need to be updated: - input_queue_tail - input_pkt_queue (next, prev, qlen, lock) - backlog.state (if input_pkt_queue was empty) Unfortunately they are currenly using two cache lines: /* --- cacheline 3 boundary (192 bytes) --- */ call_single_data_t csd __attribute__((__aligned__(64))); /* 0xc0 0x20 */ struct softnet_data * rps_ipi_next; /* 0xe0 0x8 */ unsigned int cpu; /* 0xe8 0x4 */ unsigned int input_queue_tail; /* 0xec 0x4 */ struct sk_buff_head input_pkt_queue; /* 0xf0 0x18 */ /* --- cacheline 4 boundary (256 bytes) was 8 bytes ago --- */ struct napi_struct backlog __attribute__((__aligned__(8))); /* 0x108 0x1f0 */ Add one ____cacheline_aligned_in_smp to make sure they now are using a single cache line. Also, because napi_struct has written fields, make @state its first field. We want to make sure that cpus adding packets to sd->input_pkt_queue are not slowing down cpus processing their backlog because of false sharing. After this patch new layout is: /* --- cacheline 5 boundary (320 bytes) --- */ long int pad[3] __attribute__((__aligned__(64))); /* 0x140 0x18 */ unsigned int input_queue_tail; /* 0x158 0x4 */ /* XXX 4 bytes hole, try to pack */ struct sk_buff_head input_pkt_queue; /* 0x160 0x18 */ struct napi_struct backlog __attribute__((__aligned__(8))); /* 0x178 0x1f0 */ Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com> Link: https://patch.msgid.link/20251024091240.3292546-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.