Re: [Linaro-acpi] [PATCH 4/4] acpi: cppc: replace writeX/readX to PCC with relaxed version

On 15 January 2016 at 13:43, Prashanth Prakash pprakash@codeaurora.org wrote:

We do not have a strict read/write order requirement while accessing PCC subspace. The only requirement is all access should be committed before triggering the PCC doorbell to transfer the ownership of PCC to the platform and this requirement is enforced by the PCC driver.

Profiling on a many core system shows improvement of about 1.8us on average per freq change request(about 10% improvement on average). Since these operations are executed while holding the pcc_lock, reducing this time helps the CPPC implementation to scale much better as the number of cores increases.

Signed-off-by: Prashanth Prakash pprakash@codeaurora.org

drivers/acpi/cppc_acpi.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-)

Acked-by: Ashwin Chaugule ashwin.chaugule@linaro.org

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c index b85759d..87936d7 100644 --- a/drivers/acpi/cppc_acpi.c +++ b/drivers/acpi/cppc_acpi.c @@ -119,10 +119,10 @@ static int send_pcc_cmd(u16 cmd) }

    /* Write to the shared comm region. */

•   writew(cmd, &generic_comm_base->command);
  

•   writew_relaxed(cmd, &generic_comm_base->command);
  
    /* Flip CMD COMPLETE bit */
  

•   writew(0, &generic_comm_base->status);
  

•   writew_relaxed(0, &generic_comm_base->status);
  
    /* Ring doorbell */
    ret = mbox_send_message(pcc_channel, &cmd);
  

@@ -604,16 +604,16 @@ static int cpc_read(struct cpc_reg *reg, u64 *val)

            switch (reg->bit_width) {
            case 8:

•                   *val = readb(vaddr);
  

•                   *val = readb_relaxed(vaddr);
                    break;
            case 16:
  

•                   *val = readw(vaddr);
  

•                   *val = readw_relaxed(vaddr);
                    break;
            case 32:
  

•                   *val = readl(vaddr);
  

•                   *val = readl_relaxed(vaddr);
                    break;
            case 64:
  

•                   *val = readq(vaddr);
  

•                   *val = readq_relaxed(vaddr);
                    break;
            default:
                    pr_debug("Error: Cannot read %u bit width from PCC\n",
  

@@ -635,16 +635,16 @@ static int cpc_write(struct cpc_reg *reg, u64 val)

            switch (reg->bit_width) {
            case 8:

•                   writeb(val, vaddr);
  

•                   writeb_relaxed(val, vaddr);
                    break;
            case 16:
  

•                   writew(val, vaddr);
  

•                   writew_relaxed(val, vaddr);
                    break;
            case 32:
  

•                   writel(val, vaddr);
  

•                   writel_relaxed(val, vaddr);
                    break;
            case 64:
  

•                   writeq(val, vaddr);
  

•                   writeq_relaxed(val, vaddr);
                    break;
            default:
                    pr_debug("Error: Cannot write %u bit width to PCC\n",
  

-- Qualcomm Technologies, Inc. on behalf of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.