svn commit: r286320 - head/sys/cam/ctl

[Steven Hartland]

Nice!!

On 05/08/2015 14:46, Alexander Motin wrote:
> Author: mav
> Date: Wed Aug  5 13:46:15 2015
> New Revision: 286320
> URL: https://svnweb.freebsd.org/changeset/base/286320
>
> Log:
>    Issue all reads of single XCOPY segment simultaneously.
>    
>    During vMotion and Clone VMware by default runs multiple sequential 4MB
>    XCOPY requests same time.  If CTL issues reads sequentially in 1MB chunks
>    for each XCOPY command, reads from different commands are not detected
>    as sequential by serseq option code and allowed to execute simultaneously.
>    Such read pattern confused ZFS prefetcher, causing suboptimal disk access.
>    Issuing all reads same time make serseq code work properly, serializing
>    reads both within each XCOPY command and between them.
>    
>    My tests with ZFS pool of 14 disks in RAID10 shows prefetcher efficiency
>    improved from 37% to 99.7%, copying speed improved by 10-60%, average
>    read latency reduced twice on HDD layer and by five times on zvol layer.
>    
>    MFC after:	2 weeks
>    Sponsored by:	iXsystems, Inc.
>
> Modified:
>    head/sys/cam/ctl/ctl_tpc.c
>
> Modified: head/sys/cam/ctl/ctl_tpc.c
> ==============================================================================
> --- head/sys/cam/ctl/ctl_tpc.c	Wed Aug  5 13:10:13 2015	(r286319)
> +++ head/sys/cam/ctl/ctl_tpc.c	Wed Aug  5 13:46:15 2015	(r286320)
> @@ -817,7 +817,7 @@ tpc_process_b2b(struct tpc_list *list)
>   	struct scsi_ec_segment_b2b *seg;
>   	struct scsi_ec_cscd_dtsp *sdstp, *ddstp;
>   	struct tpc_io *tior, *tiow;
> -	struct runl run, *prun;
> +	struct runl run;
>   	uint64_t sl, dl;
>   	off_t srclba, dstlba, numbytes, donebytes, roundbytes;
>   	int numlba;
> @@ -889,8 +889,7 @@ tpc_process_b2b(struct tpc_list *list)
>   	list->segsectors = numbytes / dstblock;
>   	donebytes = 0;
>   	TAILQ_INIT(&run);
> -	prun = &run;
> -	list->tbdio = 1;
> +	list->tbdio = 0;
>   	while (donebytes < numbytes) {
>   		roundbytes = numbytes - donebytes;
>   		if (roundbytes > TPC_MAX_IO_SIZE) {
> @@ -942,8 +941,8 @@ tpc_process_b2b(struct tpc_list *list)
>   		tiow->io->io_hdr.ctl_private[CTL_PRIV_FRONTEND].ptr = tiow;
>   
>   		TAILQ_INSERT_TAIL(&tior->run, tiow, rlinks);
> -		TAILQ_INSERT_TAIL(prun, tior, rlinks);
> -		prun = &tior->run;
> +		TAILQ_INSERT_TAIL(&run, tior, rlinks);
> +		list->tbdio++;
>   		donebytes += roundbytes;
>   		srclba += roundbytes / srcblock;
>   		dstlba += roundbytes / dstblock;
>