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Activate write-only optimization if bpf device opened with O_WRONLY.

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dhclient opens bpf as write-only to send packets. It never reads received
packets from that descriptor, but processing them in kernel takes time.
Especially much time takes packet timestamping on systems with expensive
timecounter, such as bhyve guest, where network speed dropped in half.

MFC after:	2 weeks
Sponsored by:	iXsystems, Inc.
This commit is contained in:
Alexander Motin 2015-04-20 10:44:46 +00:00
parent d9a6698393
commit 7144875388
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=281765
1 changed files with 3 additions and 1 deletions
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4
sys/net/bpf.c
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@ -601,7 +601,7 @@ bpf_attachd(struct bpf_d *d, struct bpf_if *bp)
* Save sysctl value to protect from sysctl change
* between reads
*/
op_w = V_bpf_optimize_writers;
op_w = V_bpf_optimize_writers || d->bd_writer;
if (d->bd_bif != NULL)
bpf_detachd_locked(d);
@ -864,6 +864,8 @@ bpfopen(struct cdev *dev, int flags, int fmt, struct thread *td)
* particular buffer method.
*/
bpf_buffer_init(d);
if ((flags & FREAD) == 0)
d->bd_writer = 2;
d->bd_hbuf_in_use = 0;
d->bd_bufmode = BPF_BUFMODE_BUFFER;
d->bd_sig = SIGIO;