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Looking for Insights on Tock's Context Switch Latency
by zhiyao.ma.98＠gmail.com Oct. 17, 2024

Oct. 17, 2024

Hello Tock developers, I am recently testing Tock's context switch speed with an STM32F412G-Discovery board, and I noticed that the latency is longer than expected. I hope to confirm that my settings are correct and gain some insights behind the data. To test the context switch speed, I implemented two apps called "server" and "client." The server sets up an IPC service that simply notifies completion back to the client. The client invokes the IPC service 10,000 times in a loop and then calculates the average ping-pong time. On my board, the 10,000 ping-pong takes 10,748 ms. That is more than 1ms for each ping-pong. I believe the CPU clock is set to 96 MHz by the default kernel configuration for the board. With a similar clock speed, a ping-pong implemented through task notification on FreeRTOS takes around 13 μs, which is almost two orders of magnitude faster than Tock. Professor Campbell pointed out to me that there are multiple context switches for each ping-pong: On the "client" side: - calls command() -> context switch to the kernel - command returns -> context switch back to the client app - client app calls yield -> context switch back to the kernel Next, on the “server” side: - upcall scheduled -> context switch to the server app - calls ipc_notify_client -> context switch to the kernel to schedule the upcall - command returns -> context switch back to the server app - yield -> context switch to the kernel Finally, on the “client” side again: - upcall scheduled -> context switch to the client app However, even if there are 8 context switches per ping-pong, on average each context switch still takes around 135 μs, which is around 13k instructions executed per context switch on a 96 MHz CPU. The number still seems to be high. Below is the source code for the “server” and “client” app. Server: ```c #include <libtock/kernel/ipc.h> #include <libtock/tock.h> static void ipc_callback( int pid, __attribute__ ((unused)) int len, __attribute__ ((unused)) int buf, __attribute__ ((unused)) void* ud) { ipc_notify_client(pid); } int main(void) { ipc_register_service_callback("server", ipc_callback, NULL); while (1) { yield(); } } ``` Client: ```c #include <stdio.h> #include <libtock-sync/services/alarm.h> #include <libtock/kernel/ipc.h> size_t service_id = -1; char buf[64] __attribute__((aligned(64))); bool done = false; static void ipc_callback(__attribute__ ((unused)) int pid, __attribute__ ((unused)) int len, __attribute__ ((unused)) int arg2, __attribute__ ((unused)) void* ud) { done = true; } static uint32_t get_time_ms(void) { struct timeval tv; libtock_alarm_gettimeasticks(&tv, NULL); return (tv.tv_sec * 1000) + (tv.tv_usec / 1000); } int main(void) { int ret; ret = ipc_discover("server", &service_id); while (ret != RETURNCODE_SUCCESS) { printf("No server, retry in 1 second.\n"); libtocksync_alarm_delay_ms(1000); } printf("Server discovered.\n"); ipc_register_client_callback(service_id, ipc_callback, NULL); ipc_share(service_id, buf, 64); uint32_t start_time = get_time_ms(); for (int i = 0; i < 10000; ++i) { done = false; ipc_notify_service(service_id); yield_for(&done); } uint32_t end_time = get_time_ms(); printf("Ping-pong 10000 times take %lu ms.\n", end_time - start_time); return 0; } ```

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Re: [Spam/Phising] Notification:- Password Update
by Leon Schuermann Oct. 14, 2024

Oct. 14, 2024

"lists.tockos.org or Email Admin via Devel" <devel(a)lists.tockos.org> writes: > The password to your mailbox devel(a)lists.tockos.org has expired. Apologies for letting this email through, this is obviously phishing. The "Accept" and "Reject" buttons in the webinterface were too close together. :/

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Tock meeting agenda 2024-10-11
by Amit Levy Oct. 11, 2024

Oct. 11, 2024

Meeting Link: https://meetings.dialpad.com/room/tock/1vnk9r3e1b No agenda items today. We can add some on the call. Otherwise, I'll suggest briefly talking about clarifying invariants of the alarm stack, followed by pull request triage. Agenda - Updates - TBD

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Call for Tock meeting agenda items 2024-10-11
by Amit Levy Oct. 11, 2024

Oct. 11, 2024

Please response with proposed agenda items and +1s for tomorrows core meeting

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Discussion on u32
by Lawrence Esswood Oct. 7, 2024

Oct. 7, 2024

I think this is a good discussion for Friday, but I wanted to send out an advance email to give time for people to gather their thoughts in advance The current set of return codes include a type. e.g. calls like allow/brk currently return SyscallReturnU32U32 or SyscallReturnU32. Clearly this is not true for 64-bit platforms. Or for CHERI where the size of an address is not the size of a pointer.I think there are a few options: 1. 1) They should return different codes on different platforms: SyscallReturnu32 on 32-bit, SyscallReturnu64on 64-bit, SyscallReturnMetaPtr on CHERI etc with some meta constructors to help choose. Userspace should expect the same and be If-Defed appropriately. 2. 2) They should return a new more specific code SyscallReturnPtr / SyscallReturnUsize on all platforms, and user space should check for just that one.e 3. 3) These calls are already made type safe because of the wrappers in libtock-c / libtock-rs. Just use SyscallSuccess for these built in syscalls. Wrappers know what they are getting. 4. 4) A true evil one. Option 3, but SyscallReturnu32 is the code for legacy reasons. You know what you are actually getting. What I actually did on my fork was just 3 (because all these different codes were getting in the way), but this does break compatibility unless there is a matching change in libtock-c/libtock-rs and it would probably be better not to do so. In fact, both 2 and 3 are breaking API changes. This means that possibly we should prefer (1), simply for backwards compatibility? This is roughly what the consttructor I added for SyscallReturnUsize does: selects one of SyscallReturnu32 or SyscallReturnu64 as appropriate. But possibly we will need a few more as soon as CHERI comes into play.As for types for commands:Currently in the kernel commands are:fn command(&self, cmd_num: usize, arg1: usize, arg2: usize, appid: ProcessId) Which is already usize-ified.In libtock-c: syscall_return_t command(uint32_t driver, uint32_t command, size_t arg1, size_t arg2); There is clearly a mismatch there on command number. I am of the mind that the driver/command being u32 is fine, and args should really be usize. For instance, a command might realistically take an offset to a previously allowed buffer. This is usize, not u32.Upcalls: in the kernel were all u32, I changed most of the arguments usize apart from data/fn pointer which are MetaPtr. i.e., the type in C should be:typedef void (subscribe_upcall)(size_t, size_t, size_t, void*);where currently it istypedef void (subscribe_upcall)(int, int, int, void*);And I think its worth some discussion whether people are happy with this. It means nothing for 32-bit libtock-c because the ABI for passing usize is the same as int on 32-bit platforms. In libtock-rs I have the patches ready to go to define the upcall trait on both u32 and usize so it won't break any code there. Lawrence

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Tock meeting agenda 2024-10-04
by Amit Levy Oct. 4, 2024

Oct. 4, 2024

Meeting Link: https://meetings.dialpad.com/room/tock/1vnk9r3e1b Agenda - Updates - Pointer returns from syscalls on non-32-bit platforms (https://lists.tockos.org/hyperkitty/list/devel@lists.tockos.org/thread/ACZB…)

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Call for Tock meeting agenda items 2024-10-04
by Amit Levy Oct. 3, 2024

Oct. 3, 2024

Please response with proposed agenda items and +1s for tomorrows core meeting

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Tock meeting agenda 2024-09-27
by Amit Levy Sept. 27, 2024

Sept. 27, 2024

Meeting Link: https://meetings.dialpad.com/room/tock/1vnk9r3e1b Agenda - Updates - PR status - Raw 802.15.4 support - what to do about it? - https://github.com/tock/libtock-rs/pull/551 * Needs someone knowledgeable about libtock-rs to look at it and review * What's the bar for merging self-contained changes in libtock-rs? - PIO - how should we handle programmable I/O bytecode? https://github.com/tock/tock/pull/4179 * Example: https://github.com/tock/tock/blob/5ad547c0998320b30b0b66ee7ff799dcb65f0f0e/… * Zephyr deals with this similarly: https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/serial/uart_…

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Re: Tock meeting agenda 2024-09-27
by Branden Ghena Sept. 27, 2024

Sept. 27, 2024

A couple of last-minute, low-priority items. Raw 802.15.4 support - what to do about it? https://github.com/tock/libtock-rs/pull/551 * Needs someone knowledgeable about libtock-rs to look at it and review (this can't all fall on Jonathan's lap) * What's the bar for merging self-contained changes in libtock-rs? PIO - how should we handle programmable I/O bytecode? https://github.com/tock/tock/pull/4179 * Example: https://github.com/tock/tock/blob/5ad547c0998320b30b0b66ee7ff799dcb65f0f0e/… * Zephyr deals with this similarly: https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/serial/uart_… Thanks, Branden Ghena Northwestern University On Thu, Sep 26, 2024 at 12:46 PM Amit Levy via Devel <devel(a)lists.tockos.org> wrote: > Please response with proposed agenda items and +1s for tomorrows core > meeting > _______________________________________________ > Devel mailing list -- devel(a)lists.tockos.org > To unsubscribe send an email to devel-leave(a)lists.tockos.org >

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Tock meeting agenda 2024-09-27
by Amit Levy Sept. 26, 2024

Sept. 26, 2024

Please response with proposed agenda items and +1s for tomorrows core meeting

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