On 30 May 2018 at 04:12, Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote:
> Previously, we only throttle sending status when doing earse or
> accessing RPMB. So this patch firstly add a new flag to teach
> mmc_poll_for_busy() to relinquish CPU for the cases aforementioned,
> as mmc_poll_for_busy() is also used in performance critical path
> so that we don't want to hurt performance.
>
> However, based on the fact that the system will serve busy polling
> which could drastically hurt responsiveness if only one online CPU
> is serving the system. Then there is also an old saying that "Grasp
> all, lose all", which teach us to sacrifice a little peformance to
> gain responsiveness in this case.
>
> Summary: relinquish CPU in MP system for doing erase and accessing RPMB,
> or do it for all operations waiting for polling busy when only one CPU
> is serving for schedule.
This makes sense, however please move this patch prior patch6 (changes
for erase), as else it means that you will introduce a regression in
behavior between patch 6 and $subject patch.
Perhaps the changelog should even mentiond that the adaptive polling
behavior is inherited from the similar approach already taken by the
erase polling scheme.
>
> Signed-off-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>
>
[...]
> int mmc_poll_for_busy(struct mmc_card *card, unsigned int timeout_ms,
> bool send_status, bool retry_crc_err, bool use_r1b_resp,
> u32 *resp_status, bool check_busy(u32 device_status),
> - bool poll_for_switch)
> + bool poll_for_switch, bool relinquish_cpu)
Maybe "adaptive_poll", give a better description of the use of the parameter!?
> {
> struct mmc_host *host = card->host;
> - int err;
> + int err, loop_udelay=64, udelay_max=32768;
> unsigned long timeout;
> u32 status = 0;
> bool expired = false;
> @@ -519,7 +519,24 @@ int mmc_poll_for_busy(struct mmc_card *card, unsigned int timeout_ms,
> mmc_hostname(host), __func__);
> return -ETIMEDOUT;
> }
> - } while (busy);
> +
> + if (!busy)
> + break;
> +
> + /*
> + * Relinquish CPU unconditionally if the caller wants.
> + * Or try to do that if only one CPU is online for sched
> + * which is based on the strategy to balance response time
> + * with turnaround time.
> + */
> + if (unlikely(relinquish_cpu || num_online_cpus() == 1)) {
> + usleep_range(loop_udelay, loop_udelay << 1);
> + if (loop_udelay < udelay_max)
> + loop_udelay <<= 1;
> + }
> +
> +
> + } while (1);
>
> return 0;
> }
> @@ -598,7 +615,7 @@ int __mmc_switch(struct mmc_card *card, u8 set, u8 index, u8 value,
> /* Let's try to poll to find out when the command is completed. */
> err = mmc_poll_for_busy(card, timeout_ms, send_status, retry_crc_err,
> use_r1b_resp, NULL, &mmc_switch_in_prg_state,
> - true);
> + true, false);
> if (err)
> goto out;
>
> diff --git a/drivers/mmc/core/mmc_ops.h b/drivers/mmc/core/mmc_ops.h
> index 8830c1d..4a30a81 100644
> --- a/drivers/mmc/core/mmc_ops.h
> +++ b/drivers/mmc/core/mmc_ops.h
> @@ -36,7 +36,7 @@
> int mmc_poll_for_busy(struct mmc_card *card, unsigned int timeout_ms,
> bool send_status, bool retry_crc_err, bool use_r1b_resp,
> u32 *resp_status, bool check_busy(u32 device_status),
> - bool poll_for_switch);
> + bool poll_for_switch, bool relinquish_cpu);
> int mmc_switch_status(struct mmc_card *card);
> int __mmc_switch_status(struct mmc_card *card, bool crc_err_fatal);
> int __mmc_switch(struct mmc_card *card, u8 set, u8 index, u8 value,
> --
> 1.9.1
>
>
Kind regards
Uffe
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