Tweak QSPI FIFO_THRESH - #2679
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Sorry, just to clarify, are the second two runs in the PR description both with Edit: ah, after looking at the PR, i think i know the value lol: |
hawkw
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Sep 10, 2026
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| const FIFO_SIZE: usize = 32; | ||
| const FIFO_THRESH: usize = 16; | ||
| const FIFO_THRESH: usize = 1; |
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a comment describing why we set this to 1 might be nice here, but i suppose it's in the commit history.
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The QPSI hardware has an internal FIFO with a configurable threshold to generate an interrupt. We currently have it set to 16 (50%). This results in many context switches because we wait for an interrupt when it drops below that threshold. Turning it down improves performance at the cost of blocking for longer periods of time. Baseline laura@cadbury ~ $ time pfexec humility -t c71 -a ~/build-gimlet-c-lab-image-default.zip hiffy -c HostFlash.hash -aaddress=0,len=33554432 --timeout 1000000 humility: WARNING: archive on command-line overriding archive in environment file humility: attached to 0483:3754:001100184741500820383733 via ST-Link V3 HostFlash.hash() => [ 0x9c, 0x41, 0xaf, 0x46, 0x10, 0xb8, 0x55, 0x1f, 0x28, 0x5a, 0xf6, 0xbe, 0xd7, 0x84, 0x2c, 0xab, 0xc6, 0xa4, 0x2a, 0xf4, 0x90, 0x93, 0x88, 0x8a, 0xc9, 0x61, 0x39, 0xf3, 0xde, 0xee, 0x86, 0x1d ] real 0m7.480s user 0m3.315s sys 0m0.562s FIFO_THRESH 8 laura@cadbury ~ $ time pfexec humility -t c71 -a ~/build-gimlet-c-lab-image-default.zip hiffy -c HostFlash.hash -aaddress=0,len=33554432 --timeout 1000000 humility: WARNING: archive on command-line overriding archive in environment file humility: attached to 0483:3754:001100184741500820383733 via ST-Link V3 HostFlash.hash() => [ 0x9c, 0x41, 0xaf, 0x46, 0x10, 0xb8, 0x55, 0x1f, 0x28, 0x5a, 0xf6, 0xbe, 0xd7, 0x84, 0x2c, 0xab, 0xc6, 0xa4, 0x2a, 0xf4, 0x90, 0x93, 0x88, 0x8a, 0xc9, 0x61, 0x39, 0xf3, 0xde, 0xee, 0x86, 0x1d ] real 0m6.504s user 0m3.235s sys 0m0.498s FIFO_THRESH 4 laura@cadbury ~ $ time pfexec humility -t c71 -a ~/build-gimlet-c-lab-image-default.zip hiffy -c HostFlash.hash -aaddress=0,len=33554432 --timeout 1000000 humility: WARNING: archive on command-line overriding archive in environment file humility: attached to 0483:3754:001100184741500820383733 via ST-Link V3 HostFlash.hash() => [ 0x9c, 0x41, 0xaf, 0x46, 0x10, 0xb8, 0x55, 0x1f, 0x28, 0x5a, 0xf6, 0xbe, 0xd7, 0x84, 0x2c, 0xab, 0xc6, 0xa4, 0x2a, 0xf4, 0x90, 0x93, 0x88, 0x8a, 0xc9, 0x61, 0x39, 0xf3, 0xde, 0xee, 0x86, 0x1d ] real 0m6.480s user 0m3.242s sys 0m0.495s laura@cadbury ~ $ time pfexec humility -t c71 -a ~/build-gimlet-c-lab-image-default.zip hiffy -c HostFlash.hash -aaddress=0,len=33554432 --timeout 1000000 humility: WARNING: archive on command-line overriding archive in environment file humility: attached to 0483:3754:001100184741500820383733 via ST-Link V3 HostFlash.hash() => [ 0x9c, 0x41, 0xaf, 0x46, 0x10, 0xb8, 0x55, 0x1f, 0x28, 0x5a, 0xf6, 0xbe, 0xd7, 0x84, 0x2c, 0xab, 0xc6, 0xa4, 0x2a, 0xf4, 0x90, 0x93, 0x88, 0x8a, 0xc9, 0x61, 0x39, 0xf3, 0xde, 0xee, 0x86, 0x1d ] real 0m6.196s user 0m3.210s sys 0m0.485s
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The QPSI hardware has an internal FIFO with a configurable threshold to generate an interrupt. We currently have it set to 16 (50%). This results in many context switches because we wait for an interrupt when it drops below that threshold. Turning it down improves performance at the cost of blocking for longer periods of time.
Baseline
laura@cadbury ~ $ time pfexec humility -t c71 -a ~/build-gimlet-c-lab-image-default.zip hiffy -c HostFlash.hash -aaddress=0,len=33554432 --timeout 1000000 humility: WARNING: archive on command-line overriding archive in environment file humility: attached to 0483:3754:001100184741500820383733 via ST-Link V3 HostFlash.hash() => [ 0x9c, 0x41, 0xaf, 0x46, 0x10, 0xb8, 0x55, 0x1f, 0x28, 0x5a, 0xf6, 0xbe, 0xd7, 0x84, 0x2c, 0xab, 0xc6, 0xa4, 0x2a, 0xf4, 0x90, 0x93, 0x88, 0x8a, 0xc9, 0x61, 0x39, 0xf3, 0xde, 0xee, 0x86, 0x1d ]
real 0m7.480s
user 0m3.315s
sys 0m0.562s
FIFO_THRESH 8
laura@cadbury ~ $ time pfexec humility -t c71 -a ~/build-gimlet-c-lab-image-default.zip hiffy -c HostFlash.hash -aaddress=0,len=33554432 --timeout 1000000 humility: WARNING: archive on command-line overriding archive in environment file humility: attached to 0483:3754:001100184741500820383733 via ST-Link V3 HostFlash.hash() => [ 0x9c, 0x41, 0xaf, 0x46, 0x10, 0xb8, 0x55, 0x1f, 0x28, 0x5a, 0xf6, 0xbe, 0xd7, 0x84, 0x2c, 0xab, 0xc6, 0xa4, 0x2a, 0xf4, 0x90, 0x93, 0x88, 0x8a, 0xc9, 0x61, 0x39, 0xf3, 0xde, 0xee, 0x86, 0x1d ]
real 0m6.504s
user 0m3.235s
sys 0m0.498s
FIFO_THRESH 4
laura@cadbury ~ $ time pfexec humility -t c71 -a ~/build-gimlet-c-lab-image-default.zip hiffy -c HostFlash.hash -aaddress=0,len=33554432 --timeout 1000000 humility: WARNING: archive on command-line overriding archive in environment file humility: attached to 0483:3754:001100184741500820383733 via ST-Link V3 HostFlash.hash() => [ 0x9c, 0x41, 0xaf, 0x46, 0x10, 0xb8, 0x55, 0x1f, 0x28, 0x5a, 0xf6, 0xbe, 0xd7, 0x84, 0x2c, 0xab, 0xc6, 0xa4, 0x2a, 0xf4, 0x90, 0x93, 0x88, 0x8a, 0xc9, 0x61, 0x39, 0xf3, 0xde, 0xee, 0x86, 0x1d ]
real 0m6.480s
user 0m3.242s
sys 0m0.495s
laura@cadbury ~ $ time pfexec humility -t c71 -a ~/build-gimlet-c-lab-image-default.zip hiffy -c HostFlash.hash -aaddress=0,len=33554432 --timeout 1000000 humility: WARNING: archive on command-line overriding archive in environment file humility: attached to 0483:3754:001100184741500820383733 via ST-Link V3 HostFlash.hash() => [ 0x9c, 0x41, 0xaf, 0x46, 0x10, 0xb8, 0x55, 0x1f, 0x28, 0x5a, 0xf6, 0xbe, 0xd7, 0x84, 0x2c, 0xab, 0xc6, 0xa4, 0x2a, 0xf4, 0x90, 0x93, 0x88, 0x8a, 0xc9, 0x61, 0x39, 0xf3, 0xde, 0xee, 0x86, 0x1d ]
real 0m6.196s
user 0m3.210s
sys 0m0.485s