Messages in this thread Patch in this message | | | From | Yu Kuai <> | Subject | Why is MEGASAS_SAS_QD set to 256? | Date | Thu, 24 Nov 2022 11:45:16 +0800 |
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Hi,
While upgrading kernel from 4.19 to 5.10, I found that fio 1 thread 4k sequential io performance is dropped(160Mib -> 100 Mib), root cause is that queue_depth is changed from 64 to 256.
commit 6e73550670ed1c07779706bb6cf61b99c871fc42 scsi: megaraid_sas: Update optimal queue depth for SAS and NVMe devices
diff --git a/drivers/scsi/megaraid/megaraid_sas.h b/drivers/scsi/megaraid/megaraid_sas.h index bd8184072bed..ddfbe6f6667a 100644 --- a/drivers/scsi/megaraid/megaraid_sas.h +++ b/drivers/scsi/megaraid/megaraid_sas.h @@ -2233,9 +2233,9 @@ enum MR_PD_TYPE {
/* JBOD Queue depth definitions */ #define MEGASAS_SATA_QD 32 -#define MEGASAS_SAS_QD 64 +#define MEGASAS_SAS_QD 256 #define MEGASAS_DEFAULT_PD_QD 64 -#define MEGASAS_NVME_QD 32 +#define MEGASAS_NVME_QD 64
And with the default nr_requests 256, 256 queue_depth will make the elevator has no effect, specifically io can't be merged in this test case. Hence it doesn't make sense to me to set default queue_depth to 256.
Is there any reason why MEGASAS_SAS_QD is changed to 64? Thanks, Kuai
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