Historically, the loopback driver used the largest packet size of all enabled link layer protocols. This permitted packets to be forward via the loopbak device with no major loss of performance. However, in experimenting with configurations where no other link layer protocols were enabled, this means the loopback packet size was set to the smallest possible size, to the SLIP minimum of 296 bytes. This resulted in terrible loopback performance.
This commit adds an option to increase the loopback packet size with the option CONFIG_NET_LOOPBACK_PACKETSIZE.
The loopback driver packet buffer should be quite large. The larger the loopback packet buffer, the better will be TCP performance of the loopback transfers. The Linux loopback device historically used packet buffers of size 16Kb, but that was increased in recent Linux versions to 64Kb. Those sizes may be excessive for resource constrained MCUs, however.
The network still enforces the lower limit that is the maximum packet size of all enabled link layer protocols. But this new option permits the loopback packet size to be increased from that.
* net/Kconfig: Adds CONFIG_NET_LOOPBACK_PKTSIZE option
* include/nuttx/net/netconfig.h: Assures that the packet size that is used is at least as large as the largest packet size of other link layer protocols.
* drivers/net/loopback.c: Use that larger packet size.
* boards/sim/sim/sim/configs/tcploop/defconfig: Set the loopback packet size to 1500
To avoid ps generate "Segmentation fault" because do_stackcheck
check the stack color if the stack size doesn't equal zero
BTW, it is better to set idle task stack size to zero since idle
task use the host thread and the stack size from config isn't the
actual value.
The benefits include:
1. Simplify the implementation
2. Support Ctrl+C automatically
3. Support poll automatically
4. Call pm_activity automatically
5. Save one polling thread
Call xxx_timer_initialize from clock subsystem to make timer ready for use as soon as possiblei and revert the workaround:
commit 0863e771a9
Author: Gregory Nutt <gnutt@nuttx.org>
Date: Fri Apr 26 07:24:57 2019 -0600
Revert "sched/clock/clock_initialize.c: clock_inittime() needs to be done with CONFIG_SCHED_TICKLESS and clock_initialize should skip clock_inittime() for external RTC case since the RTC isn't ready yet."
This reverts commit 2bc709d4b9.
Commit 2bc709d4b9 was intended to handle the case where up_timer_gettime may not start from zero case. However, this change has the side-effect of breaking every implementation of tickless mode: After this change the tickless timer structures are used before they are initialized in clock_inittime(). Initialization happens later when up_initialize is called() when arm_timer_initialize().
Since the tickless mode timer is very special, one solution might be to
1. Rename xxx_timer_initialize to up_timer_initialize
2 Move up_timer_initialize to include/nuttx/arch.h
3. Call it from clock subsystem instead up_initialize
Basically, this change make timer initialization almost same as rtc initialization(up_rtc_initialize).
For now, however, we just need to revert the change.
