[OpenWrt-Devel] Why OpenWrt sucks?
zefir.kurtisi at neratec.com
Wed Mar 11 08:12:37 EDT 2015
On 03/10/2015 10:39 PM, Felix Fietkau wrote:
> On 2015-03-10 20:22, Zefir Kurtisi wrote:
>> This gives at least two sources for optimization for the reference driver: 1) save
>> inter-layer processing overhead (passing commands from hostapd directly to HW is
>> cheaper than passing it through 4 layers), and 2) vastly reduce locking when you
>> are in full control of concurrency.
> The overhead of commands issued by hostapd is pretty much irrelevant.
> All that matters for driver performance is the actual data path (network
> stack, mac80211 tx/rx, driver tx/rx).
> Also, I've not seen any indication in my tests that locking is a
> measurable cause of performance issues.
> When it comes to performance issues, guesswork is meaningless,
> measurements (e.g. profiling results) matter!
> - Felix
Hm, maybe my memory is deceiving me, but I'm pretty sure my statement is not based
on guesswork but in fact on measurements.
Like 3 years ago, for a PPC based platform we had to decide whether to go with the
reference driver or with aht9k. For that, thorough performance measurements were
performed and ath9k was somewhere between 10 and 30% behind throughput wise.
Guessing that synchronization might be one factor, we removed locking in ath9k and
results improved noticeably by up to 5%. At that time and on a PPC platform it was
a factor, it might be irrelevant today. I remember it well since it indicated that
ath9k has some optimization potential left and we finally decided for it.
Anyway, that was not my point here. What I claim is that a proprietary driver
always opens more optimization potential (cross-layer wise).
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