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To insert or encapsulate a packet with an SRH, we need a large enough skb headroom. Currently, we are using pskb_expand_head to inconditionally increase the size of the headroom by the amount needed by the SRH (and IPv6 header). If this reallocation is performed by another CPU than the one that initially allocated the skb, then when the initial CPU kfree the skb, it will enter the __slab_free slowpath, impacting performances. This patch replaces pskb_expand_head with skb_cow_head, that will reallocate the skb head only if the headroom is not large enough. Performances for SRH encapsulation before the patch: Result: OK: 7348320(c7347271+d1048) usec, 5000000 (1000byte,0frags) 680427pps 5443Mb/sec (5443416000bps) errors: 0 Performances after the patch: Result: OK: 5656067(c5655678+d388) usec, 5000000 (1000byte,0frags) 884006pps 7072Mb/sec (7072048000bps) errors: 0 Signed-off-by: David Lebrun <david.lebrun@uclouvain.be> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.