Low perfomance when read from usb flash drive

[Artyom Mirgorodsky]

>Repeat the same test using FreeBSD -current.

>a) On the machine where it is slow.

vmstat -i ; sleep 1 ; vmstat -i
interrupt                          total       rate
irq1: atkbd0                         233          2
irq14: ata0                           85          0
irq16: vgapci0                      5377         52
irq21: hdac0 ohci0                   742          7
irq22: nfe0 ehci0                  23610        229
irq23: atapci1                      5405         52
cpu0: timer                       203959       1980
cpu1: timer                       200914       1950
Total                             440325       4275
interrupt                          total       rate
irq1: atkbd0                         234          2
irq14: ata0                           85          0
irq16: vgapci0                      5439         52
irq21: hdac0 ohci0                   742          7
irq22: nfe0 ehci0                  24621        236
irq23: atapci1                      5405         51
cpu0: timer                       205981       1980
cpu1: timer                       202937       1951
Total                             445444       4283

>I think the reduced performance can be explained by a clamp on the interrupt 
>rate around 1000 interrupts per second instead of 8000. Maybe someone has an 
>explanation for this?

You right, the interrupt rate around 1000 (1011) on this machine, but on FreeBSD 7.1 more 3000.
If it is some kind of interrupt aggregation, may be I can try to turn it off?


>b) On the machine where it is fast.

vmstat -i ; sleep 1 ; vmstat -i
interrupt                          total       rate
irq4: uart0                         4154          0
irq14: ata0                       472922          0
irq15: ata1                           26          0
irq18: em0                        752711          0
irq21: ahc0                           53          0
irq23: ehci0                      103456          0
irq24: em1                           147          0
cpu0: timer                   1551216517       2000
cpu1: timer                   1551195251       2000
Total                         3103745237       4001
interrupt                          total       rate
irq4: uart0                         4154          0
irq14: ata0                       472923          0
irq15: ata1                           26          0
irq18: em0                        752713          0
irq21: ahc0                           53          0
irq23: ehci0                      110949          0
irq24: em1                           147          0
cpu0: timer                   1551218551       2000
cpu1: timer                   1551197285       2000
Total                         3103756801       4001