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A significant amount of cpu cycles is spent in fq_gc()
When fq_gc() does its lookup in the rb-tree, it needs the
following fields from struct fq_flow :
f->sk (lookup key in the rb-tree)
f->fq_node (anchor in the rb-tree)
f->next (used to determine if the flow is detached)
f->age (used to determine if the flow is candidate for gc)
This unfortunately spans two cache lines (assuming 64 bytes cache lines)
We can avoid using f->next, if we use the low order bit of f->{age|tail}
This low order bit is 0, if f->tail points to an sk_buff.
We set the low order bit to 1, if the union contains a jiffies value.
Combined with the following patch, this makes sure we only need
to bring into cpu caches one cache line per flow.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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 Restructured Text 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.