getting some work done today on a Raspberry Pi 3. CPU throughput seems decent but it's still way laggy, maybe FS on microsd card sucks?
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Replying to @johnregehr
SD cards are really slow, capping at about 20 Mbit/sec. If it's over spi bus, Linux's spi overhead makes it even worse.
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Replying to @RichFelker @johnregehr
Actually according to WP, microSD can go up to 50 MHz (50 Mbit/sec) over normal 1-bit SPI. Still slow & Linux makes it slower.
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Replying to @RichFelker @johnregehr
AFAICT there's literally a scheduler round-trip for every 512-byte sector transfer, ...
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Replying to @RichFelker @johnregehr
...even if a dma-capable spi master could queue 1000s of them in principle. Yields latency between every pair of sectors.
3:30 PM - 7 Dec 2016
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