On 2024-08-22 09:40:21 +0300, Moshe Shemesh wrote: > > > On 8/21/2024 1:27 AM, Mohamed Khalfella wrote: > > > > On 2024-08-20 12:09:37 +0200, Przemek Kitszel wrote: > >> On 8/19/24 23:42, Mohamed Khalfella wrote: > >>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/pci_vsc.c b/drivers/net/ethernet/mellanox/mlx5/core/lib/pci_vsc.c > >>> index d0b595ba6110..377cc39643b4 100644 > >>> --- a/drivers/net/ethernet/mellanox/mlx5/core/lib/pci_vsc.c > >>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/pci_vsc.c > >>> @@ -191,6 +191,7 @@ static int mlx5_vsc_wait_on_flag(struct mlx5_core_dev *dev, u8 expected_val) > >>> if ((retries & 0xf) == 0) > >>> usleep_range(1000, 2000); > >>> > >>> + cond_resched(); > >> > >> the sleeping logic above (including what is out of git diff context) is > >> a bit weird (tight loop with a sleep after each 16 attempts, with an > >> upper bound of 2k attempts!) > >> > >> My understanding of usleep_range() is that it puts process to sleep > >> (and even leads to sched() call). > >> So cond_resched() looks redundant here. > > > > This matches my understanding too. usleep_range() should put the thread > > to sleep, effectively releasing the cpu to do other work. The reason I > > put cond_resched() here is that pci_read_config_dword() might take long > > time when that card sees fatal errors. I was not able to reproduce this > > so I am okay with removing this cond_resched(). > > > >> > >>> } while (flag != expected_val); > >>> > >>> return 0; > >>> @@ -280,6 +281,7 @@ int mlx5_vsc_gw_read_block_fast(struct mlx5_core_dev *dev, u32 *data, > >>> return read_addr; > >>> > >>> read_addr = next_read_addr; > >>> + cond_resched(); > >> > >> Would be great to see how many registers there are/how long it takes to > >> dump them in commit message. > >> My guess is that a single mlx5_vsc_gw_read_fast() call is very short and > >> there are many. With that cond_resched() should be rather under some > > > > I did some testing on ConnectX-5 Ex MCX516A-CDAT and here is what I saw: > > > > - mlx5_vsc_gw_read_block_fast() was called with length = 1310716 > > - mlx5_vsc_gw_read_fast() does 4 bytes at a time but the did not read > > full 1310716 bytes. Instead it was called 53813 times only. There are > > jumps in read_addr. > > - On average mlx5_vsc_gw_read_fast() took 35284.4ns > > - In total mlx5_vsc_wait_on_flag() called vsc_read() 54707 times with > > average runtime of 17548.3ns for each call. In some instances vsc_read() > > was called more than once until mlx5_vsc_wait_on_flag() returned. Mostly > > one time, but I saw 5, 8, and in one instance 16 times. As expected, > > the thread released the cpu after 16 iterations. > > - Total time to read the dump was 35284.4ns * 53813 ~= 1.898s > > > >> if (iterator % XXX == 0) condition. > > > > Putting a cond_resched() every 16 register reads, similar to > > mlx5_vsc_wait_on_flag(), should be okay. With the numbers above, this > > will result in cond_resched() every ~0.56ms, which is okay IMO. > > Sorry for the late response, I just got back from vacation. > All your measures looks right. > crdump is the devlink health dump of mlx5 FW fatal health reporter. > In the common case since auto-dump and auto-recover are default for this > health reporter, the crdump will be collected on fatal error of the mlx5 > device and the recovery flow waits for it and run right after crdump > finished. > I agree with adding cond_resched(), but I would reduce the frequency, > like once in 1024 iterations of register read. > mlx5_vsc_wait_on_flag() is a bit different case as the usleep there is > after 16 retries waiting for the value to change. > Thanks. Thanks for taking a look. Once in every 1024 iterations approximately translates to 35284.4ns * 1024 ~= 36.1ms, which is relatively long time IMO. How about any power-of-two <= 128 (~4.51ms)?
