Re: Re: [PATCH net-next] net/packet: fix TPACKET_V3 performance issue in case of TSO

On Wed, Mar 25, 2020 at 10:46 AM yang_y_yi [off-list ref] wrote:

Yes, hrtimer is better, but it will change current API semantics.

req.tp_retire_blk_tov means millisecond, if we change it as microsecond, it will break ABI.

That can be resolved by adding a new feature flag that reinterprets
the field in the request.

#define TP_FT_REQ_USEC      0x2

Please remember to use plain text and don't top paste.

At 2020-03-25 22:37:59, "Willem de Bruijn" [off-list ref] wrote:

quoted

On Wed, Mar 25, 2020 at 10:10 AM [off-list ref] wrote:

quoted

From: Yi Yang <redacted>

TPACKET_V3 performance is very very bad in case of TSO, it is even
worse than non-TSO case. For Linux kernels which set CONFIG_HZ to
1000, req.tp_retire_blk_tov = 1 can help improve it a bit, but some
Linux distributions set CONFIG_HZ to 250, so req.tp_retire_blk_tov = 1
actually means req.tp_retire_blk_tov = 4, it won't have any help.

This fix patch can fix the aforementioned performance issue, it can
boost the performance from 3.05Gbps to 16.9Gbps, a very huge
improvement. It will retire current block as early as possible in
case of TSO in order that userspace application can consume it
in time.

Signed-off-by: Yi Yang <redacted>

I'm not convinced that special casing TSO packets is the right solution here.

We should consider converting TPACKET_V3 to hrtimer and allow usec
resolution block timer.

Would that solve your issue?