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net-zerocopy: Copy straggler unaligned data for TCP Rx. zerocopy.

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[ Upstream commit 18fb76ed53865c1b5d5f0157b1b825704590beb5 ]

When TCP receive zerocopy does not successfully map the entire
requested space, it outputs a 'hint' that the caller should recvmsg().

Augment zerocopy to accept a user buffer that it tries to copy this
hint into - if it is possible to copy the entire hint, it will do so.
This elides a recvmsg() call for received traffic that isn't exactly
page-aligned in size.

This was tested with RPC-style traffic of arbitrary sizes. Normally,
each received message required at least one getsockopt() call, and one
recvmsg() call for the remaining unaligned data.

With this change, almost all of the recvmsg() calls are eliminated,
leading to a savings of about 25%-50% in number of system calls
for RPC-style workloads.

Signed-off-by: Arjun Roy <arjunroy@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Arjun Roy
2020-12-02 14:53:42 -08:00
committed by Greg Kroah-Hartman
parent 8da80ec6d4
commit 5f7aadf03f
2 changed files with 70 additions and 16 deletions
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2
include/uapi/linux/tcp.h
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@@ -349,5 +349,7 @@ struct tcp_zerocopy_receive {
__u32 recv_skip_hint; /* out: amount of bytes to skip */
__u32 inq; /* out: amount of bytes in read queue */
__s32 err; /* out: socket error */
__u64 copybuf_address; /* in: copybuf address (small reads) */
__s32 copybuf_len; /* in/out: copybuf bytes avail/used or error */
};
#endif /* _UAPI_LINUX_TCP_H */