| > Test Tree Inventory
| > ===================
| >
| > [CCID3]: Ignore trivial amounts of elapsed time
|
| Applied, but I think we can revisit elapsed time later by taking a
| timestamp earlier, at dccp_v4_rcv, because then there can be time spent
| in sk_backlog, etc. We could then store a timestamp on skb->cb and the
| ccids would set a flag on dccp_sock to tell that the timestamp is
| wanted.
|
The elapsed time is needed for RTT measurements and you are right, the
hole RTT measurement issue needs more work. And this includes CCID2
which goes into the other extreme and uses a coarse-grained HZ
resolution of RTTs. But ever since there was the issue with interface
timestamps (skb_get_timestamp) I got convinced that it is not useful
to increase the resolution below, say, 1 millisecond. (There was a
discussion with Ian about above patch where this came up.) The reason
is that when we do such fine-grained resolution, we also get a lot of
noise: much of the TCP code works very well with just the jiffies
resolution.
With regard to your point, I think it would be ideal to use timestamps
in the TCP High-Speed way (RFC 1323), where we could use a resolution of
0.00001 seconds (dccp_timestamp() and RFC 4340, 13.). That is still
very high-resolution when considering that the RFC2988 remarks regarding
clock granularity in part referred back to that old BSD timer which had
a 0.5 second granularity.
I agree fully with your suggestion: all CCID-specific RTT measurement
code can be eliminated once there is a working alternative. The
challenge that needs to be overcome is to make the timestamp usage robust
against packet duplication and re-ordering.
| Just moving ccid3hcrx_bytes_recv to after ccid3hcrx_tfrc we can save 8
| bytes.
This is good news - with regard to the above I still have in the back of
my mind that there are unused icsk fields which may also be used for
storing timestamps; this could help (in a future effort) to reduce further.
| > 2. Main CCID3 patch set
| > -----------------------
| > This is the original CCID3 patch set, developed in Feb/Mar, significantly reordered to
| > make the test tree fully bisectable.
| > The patch set does three things (reflected in the order of batches):
| >
| > (1) new TX history for TFRC (packet_history.{c,h}),
|
| Why do we need DECLARE_TFRC_TX_CACHE?
|
It is not needed for compilation. When I first did this patch set there were three different
kmem_caches defined in ccid3.c:
* one for the TX history (packet_history.c; for which the above macro was declared),
* one for the RX history (packet_history.c)
* one for the Loss History (loss_interval.c)
The loss interval history has since gone, this was done when you worked on Ian's patch set
around March/April. When the patch set is fully applied, the RX history cache also goes,
since the new patch set uses at most 4 entries per socket which are supplied by a static
kmem_cache in packet_history.c.
Long story, short conclusion: if you think this is an eyesore, feel free to take it out. I
left it in since I thought it would make the purpose clearer (since ctags then automatically
jumps to packet_history.h).
| > [TFRC]: New RX history implementation
|
|
| +static struct kmem_cache *tfrcxh;
|
| Why "xh"?
|
This is a typo, my mistake. I had meant to use the suffix `rxh' to indicate that
this static cache is for the RX history, but it somehow merged with `r'
from tfrc. Are you okay with tfrc_rxh? I will uploaded a revised patch
which uses this identifier instead. Thank you for pointing this out.
Gerrit
-
To unsubscribe from this list: send the line "unsubscribe dccp" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
