Messages in this thread | | | Date | Wed, 17 Aug 2011 18:18:39 -0600 | From | Asai Thambi S P <> | Subject | Re: [PATCH v3 2/3] drivers/block/mtip32xx: Adding source for hardware related operations |
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On 8/12/2011 2:42 AM, Jens Axboe wrote: >> +/* >> + * Obtain an empty command slot. >> + * >> + * This function needs to be reentrant since it could be called >> + * at the same time on multiple CPUs. The allocation of the >> + * command slot must be atomic. >> + * >> + * @port Pointer to the port data structure. >> + * >> + * return value >> + * >= 0 Index of command slot obtained. >> + * -1 No command slots available. >> + */ >> +static int get_slot(struct mtip_port *port) >> +{ >> + int slot, i; >> + unsigned int num_command_slots = port->dd->slot_groups * 32; >> + >> + /* >> + * Try 10 times, because there is a small race here. >> + * that's ok, because it's still cheaper than a lock. >> + */ > > Might want to expand on what that race is.
find_next_zero_bit and test_and_set, in order, could be executed in different process contexts in different processor. So both(2 or more) contexts could land in choosing the same bit, but test_and_set will succeed only for one. The failing contexts will try to get the next bit in subsequent retries. This operation is cheaper than a lock.
This procedure is protected under the counting semaphore, so there is a slot request for every context that calls this routine.
Is there an equivalent of doing find_next_zero_bit and test_and_set_bit atomically?
>> +static irqreturn_t mtip_irq_handler(int irq, void *instance) >> +{ >> + struct driver_data *dd = instance; >> +#ifdef MTIP_USE_TASKLET >> + tasklet_schedule(&dd->tasklet); >> + return IRQ_HANDLED; >> +#else >> + return mtip_handle_irq(dd); >> +#endif >> +} > > Have you experimented with blk-iopoll?
Working on this. Believe this experiment could go in parallel to submission. Let us know.
>> +/* >> + * Byte-swap ATA ID strings. >> + * >> + * ATA identify data contains strings in byte-swapped 16-bit words. >> + * They must be swapped (on all architectures) to be usable as C >> strings. >> + * This function swaps bytes in-place. >> + * >> + * @buf The buffer location of the string >> + * @len The number of bytes to swap >> + * >> + * return value >> + * None >> + */ >> +static inline void ata_swap_string(u16 *buf, unsigned int len) >> +{ >> + int i; >> + for (i = 0; i < (len/2); i++) >> + be16_to_cpus(&buf[i]); >> +} > > I'm pretty sure we have the exact same thing in IDE and libata, so lets > put this somewhere we they can all use it.
Is ata.h an appropriate location? Would it be better to make this change after inclusion of this driver?
> > Overall looks very clean. If you take care of the little things > mentioned by me and Christoph, I don't see anything stopping this from > being merged for 3.2.
Appreciate your valuable feedback.
-- Regards, Asai Thambi
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