Re: [tcpm] Hystart survey of large server operators

[Neal Cardwell <[e-mail]>]

On Thu, Jul 29, 2021 at 12:40 PM Yuchung Cheng <[e-mail]> wrote:

>
>
> On Thu, Jul 29, 2021 at 9:28 AM Bob Briscoe <[e-mail]> wrote:
>
>> Yuchung,
>>
>> On 29/07/2021 00:35, Yuchung Cheng wrote:
>>
>> same experience with Chrisitian
>>
>> For more than half a decade Google traffic used Linux CUBIC Hystart. This
>> includes google.com and YouTube public Internet traffic, as well as
>> internal Google TCP traffic. When we deployed pacing around 2013 we
>> disabled the Hystart ACK-train mechanism (that Hystart++ prohibits now) as
>> it causes false SS exit. But we continued to use the stock Hystart Delay
>> mechanism. ~2014-15 we switched to BBR which uses a different startup more
>> robust to delay jitters.
>>
>>
>> [BB] You or Neal (sry can't remember which) were one of those I surveyed
>> who said they had disabled Hystart. So perhaps this was a misunderstanding
>> over the ACK-train part.
>>
> Yes this must be mis-communication. Since that was in 2018, it's either
> "we don't use hystart b/c BBR doesn't use hystart" or "we don't use hystart
> ack-train when hystart was used in Cubic before BBR".
>

Yes, my sense of our experience with CUBIC Hystart matches Yuchung's,
including the likely sources of mis-communication.

thanks,
neal